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Question why is it so easy today to build reusable rockets? Is it because the onboard cpu speed of the chips can solve more granular control problems with low l

Question why is it so easy today to build reusable rockets? Is it because the onboard cpu speed of the chips can solve more granular control problems with low latency?

kurthr 1y ago
Proof of concept. It's a lot easier to do something, if you know it can be done.
- mempko 1y ago
  I mean, SpaceX also knew it could be done since reusable rocket tests happened in the 90s.
  - kurthr 1y ago
    Don't you mean the SpaceShuttle in the 80s? or Delta Clipper which didn't reach orbit? Really, what SpaceX did was radically different from the tests in the 90s from the rockets, to the controls, to the reusability goals. Otherwise they wouldn't have built Grasshopper. Now NewGlen is kinda a knockoff of Delta Clipper, but that's a different beast.
  - mensetmanusman 1y ago
    And physics, nothing prevents the goal beyond execution.
  - hwillis 1y ago
    The DC-X was 9.1 tonnes empty and 19 tonnes full- meaning landing thrust was ~half of takeoff thrust. The Falcon 9 was 400 tonnes full and 26 tonnes empty, so takeoff thrust was >20x higher than landing thrust. That's a huge engineering difference, roughly like the difference between a car and a helicopter. The Falcon 9 was also 4x taller, meaning 16x more force to correct a lean. A little burp would send the rocket right back up in the air.
- benjiro 1y ago
  Its more about money. If you know that something can be done, and there is a potential market for such a project, it then becomes easier to get the funding. Chicken or the egg... One thing we also need to point out, is that SpaceX uses like 80% of their yearly launches, for their own communication / sat service. This gave a incentive for that investment. Is the same reason why, despite SpaceX throwing those things up constantly, there really is a big lag of competitors with reusable rockets. Its not that they where / not able to quickly get the same tech going. They simply have less market, vs what SpaceX does non-stop. So the investments are less, what in time means less fast development. SpaceX is a bit of a strange company, partially because they used a lot of the public funds to just throw shit at the wall, and see what sticks. This resulted in them caring less if a few rockets blew up, as long as they got the data for the next one with less flaws. It becomes harder when there is more oversight of that money, or risk averse investors. Then you really want to be sure that thing goes up and come back down into one piece from the first go. A lot of projects funding are heavily based upon the first or second try of something, and then (sometimes unwisely) funding is pulled if it was not a perfect success story.
  - kurthr 1y ago
    I agree, a lot is about money, but it's not like Honda is raising external funds. Getting management to agree to do anything pretty much requires guaranteed success in large organizations.
  - PaulHoule 1y ago
    Even before SpaceX started launching their own satellites in huge numbers they had a business model where they were selling the launch, not the rocket, and selling it at a fixed price, so if some small refinement saved them 5% on launch costs it went to their pockets so they had an incentive to make those small refinements. Dragon 9 was based on conservative and boring technology but it was cost optimized before it was reusable, then reusability crushed the competition. For that matter, Starship is boring. "Throw at the wall and see what sticks" isn't "trying a bunch of crazy stuff" but trying a bunch of low and medium risk things. For instance, development of the Space Shuttle thermal tiles was outrageously expensive and resulted in a system that was outrageously expensive to maintain. They couldn't change it because lives were at stake. With Starship they can build a thermal protection system which is 90% adequate and make little changes that get it up to 100% adequate and then look at optimizing weight, speed of reuse and all that. If some of them burn up it is just money since there won't be astronauts riding it until it is perfected.
- PaulHoule 1y ago
  Also psychology and politics kept people from following the easy path. The Space Shuttle was wrong in so many ways, not least that it was a "pickup truck" as opposed to a dedicated manned vehicle (with appropriate safety features) or a dedicated cargo vehicle. Because they couldn't do unmanned tests they were stuck with the barely reusable thermal tiles and couldn't replace them with something easier to reuse (or safer!) Attempts at second generation reusable vehicles failed because rather than "solving reuse" they were all about single-stage to orbit (SSTO) [2] and aerospike engines and exotic composite materials that burned up the money/complexity/risk/technology budgets. There was a report that came out towards the end of the SDI [3] phase that pointed out the path that SpaceX followed with Dragon 9 where you could make rather ordinary rockets and reuse the first stage but expend the second because the first stage is most of the expense. They thought psychology and politics would preclude that and that people would be seduced by SSTO, aerospikes, composites, etc. Funny though out of all the design studies NASA did for the Shuttle and for heavy lift vehicles inspired by the O'Neill colony idea, there was a sketch of a "fly back booster" based on the Saturn V that would have basically been "Super Heavy" that was considered in 1979 that, retrospectively, could have given us Starship by 1990 or so. But no, we were committed to the Space Shuttle because boy the Soviet Union was intimidated by our willingness and ability to spend on senseless boondoggles! [1] The first few times the shuttle went up they were afraid the tiles would get damaged and something like the Columbia accident would happen, they made some minor changes to get them to stick better and stopped worrying, at least in public. It took 100 launches for a failure mode than affects 1% of launches to actually happen. [2] https://en.wikipedia.org/wiki/Single-stage-to-orbit https://en.wikipedia.org/wiki/Single-stage-to-orbit [3] https://en.wikipedia.org/wiki/Strategic_Defense_Initiative https://en.wikipedia.org/wiki/Strategic_Defense_Initiative (which would have required much cheaper launch)
  - EvanAnderson 1y ago
    > The Space Shuttle was wrong in so many ways, not least that it was a "pickup truck" as opposed to a dedicated manned vehicle (with appropriate safety features) or a dedicated cargo vehicle. I wonder what the STS system would have been like if the DoD's cross-range requirement hadn't been imposed.
- bookofjoe 1y ago
  See, for example: 4-minute mile
  - LeifCarrotson 1y ago
    I don't know how relevant that is. That's something that can be done by an individual, training for something slightly slower than 4 minutes and pushing through to achieve a time that onlookers might not have expected. The real friction in building a reusable rocket isn't the engineering, it's setting "let's build a reusable rocket" as a design goal, and getting a whole bunch of engineers and a whole bunch of dollars to start on that goal. You have to start with a whiteboard sketch and board-room presentation that shows it's achievable, and then send the engineers out to refine the sketch into something worth funding, and then work for months or years to build a rocket that would be a disaster if it's not achievable.
    - bookofjoe 1y ago
      >Proof of concept. It's a lot easier to do something, if you know it can be done. This. What I wanted to emphasize was how, after Bannister finally broke through the 4-minute barrier, many others did it soon after: 3 more in 1954; 4 in 1955; 3 in 1956; 5 in 1957; 4 in 1958. List: https://imgur.com/a/UadE3xa https://imgur.com/a/UadE3xa
odo1242 1y ago
I mean, it's mostly that we've decided to try to do it nowadays. Problems tend to get easier when we put hundreds of thousands of hours of work into them. It wasn't in the scope of the original rocket projects because if it was, we probably would never have launched them.
yieldcrv 1y ago
Because there’s a bigger market for space cargo I wouldn’t say anything has fundamentally changed in the rocket coordination tech itself, just the private sector being able to rationalize the cost of the trials with ROI
xeromal 1y ago
SpaceX showed it was possible and also a crappy place to work means those knowledgeable people go work elsewhere for less work and more money. inb4 blue origin / DC-X did it first
- bryanlarsen 1y ago
  Actually, the DC-X did it first, in 1993. The DC-X was the first vertical rocket landing, Blue Origin was the first vertical landing of a rocket that went to space, and SpaceX was the first vertical landing of an orbital rocket. This Honda landing neither went to space nor was orbital, so it was a similar test to the DC-X test.
  - LorenDB 1y ago
    Actually, retropeopulsive landing was demonstrated during the Apollo program, both on the moon with the LM and with LM trainers on the earth. Those systems were human controlled, of course.
- mensetmanusman 1y ago
  Crappy for 10% amazing for 90%, somewhat better than the 80/20 70/30 seen by most F500s.
  - MattRix 1y ago
    I imagine they mean crappy as in really poor work life balance.
treis 1y ago
This doesn't feel like that much of an accomplishment relatively speaking. It's a smallish rocket that went up and down. Very far away from landing something 100 times heavier from orbit.
- lupusreal 1y ago
  Nobody is propulsively landing anything from orbit yet. (Dragon is supposedly capable of it, as a backup if the chutes fail, but has never done so.)
  - xixixao 1y ago
    Starship is already pretty much there (almost-orbit and water splash)
    - lupusreal 1y ago
      They've had three failures since those earlier successes, and while I expect they'll get it eventually I wouldn't count them as doing it yet. Besides SpaceX, its also being worked on by Rocket Lab, Stoke, maybe Blue Origin, and too many Chinese companies to count.
  - deleted 1y ago
    [deleted]
FuriouslyAdrift 1y ago
They've been working on this (in cooperation with JAXA (Japan's NASA)) since 2021.
rvnx 1y ago
We now have realistic simulators like: http://orbit.medphys.ucl.ac.uk/ http://orbit.medphys.ucl.ac.uk/ -> (it's free and open-source: https://github.com/orbitersim/orbiter https://github.com/orbitersim/orbiter ) so now the main problem is building the hardware, there are a lot of solutions for the software part. Before there were no general-purpose simulators, and barely usable computers (2 MHz computer with 2 KB of memory...), so all you could do was hardcoding the path and use rather constrained algorithms.
- roshdodd 1y ago
  I don't think this was the cause. Advanced simulation capabilities have existed for many decades in the industry. Many if not most of those tools are not publicly available. I think there is also a distinction to be made between offline (engineering) and onboard computing resources. While onboard computers have been constrained in the past, control algorithms are typically simple to implement. Most of the heavy lifting (design & optimization of algorithms) is done in the R&D phase using HPC equipment.
  - nine_k 1y ago
    You can now buy vastly more computing power and do fancy fluid dynmaics, etc thanks to GPUs. 20 years ago it was much more expensive to procure, and much harder to find expertise. 30 years ago, I suppose, the field was even less mature, and limited to the few HPC installations and in-house bespoke software. Mass-produced hardware drove prices down, and availability way up, in many industries: motors, analog electronics, computers, solar panels, lithium batteries, various sensors, etc. Maybe reusable rockets, enabled by all that, are going to follow a similar trajectory as air transportation.
    - chasil 1y ago
      If we are going to be specific, 64-bit ARM (in the form of AArch64) arrived in 2011. It would seem to me that Intel and AMD were not friendly to custom designs at that time, and MIPS was not significantly evolving. A fast, low-power CPU that can access more than 4gb and is friendly to customization seems to me to be a recent development.
rsynnott 1y ago
I mean, it's been around as a concept since at least the 50s, but there was quite a lot of scepticism that it was worth the cost (this would only have been reinforced by the Shuttle, whose 'reusable' engines were a bit of a disaster)
advisedwang 1y ago
I don't know the answer, but some possibilities beyond CPU capabilities include: * Better motors for gimballing * Launch-thrust engines that throttle down low enough and preciesly enough for landing * Better materials to handle stress for flip over manover etc without added weight * More accurate position sensors * Better understanding and simulation of aerodynamics to develop body shape and write control algorithms.
- hwillis 1y ago
  Electrical engineer: motors and sensors are not really any better- motors have gotten more efficient and sensors have gotten cheaper, but gold standard sensors like ring laser gyroscopes have existed since the 60s. > Launch-thrust engines that throttle down low enough and preciesly enough for landing In large part this is due to improved simulation- spaceX made their own software: https://www.youtube.com/watch?v=ozrvfRHvYHA&t=119s https://www.youtube.com/watch?v=ozrvfRHvYHA&t=119s Experimentation was also a large factor- pintle injectors have been around for a long time, but were not used in production rockets until SpaceX (who moved from a single pintle to an annular ring). Pintle injectors are very good for throttling. > Better materials to handle stress for flip over manover etc without added weight We're still using the same materials- good ol inconel and aluminum. However 3d printing has made a pretty big difference in engines. More rockets use carbon fiber, but that isn't new exactly and the main parts are still the same variety of aluminum etc. Titanium has become more common, but is still pretty specialized- the increased availability was probably the biggest factor but improved cutting toolings (alloys and coatings) and tools (bigger, faster, less vibration) have also made a big difference.
roshdodd 1y ago
As someone who actively works in the field, it was a culmination of: - Advances in rocket engine design & tech to enable deep throttling - Control algorithms for propulsive landing maturing (Google "Lars Blackmore", "GFOLD", "Mars Landing", and work through the references) - Forward thinking and risk-taking by SpaceX to further develop tech demonstrated by earlier efforts (DC-X, Mars Landing, etc.) Modern simulation and sensor capabilities helped, but were not the major enabling factors.
- bumby 1y ago
  Can you elaborate on the advances in deep throttling?
  - 93po 1y ago
    Also didnt spacex do reuse without throttling and only having on/off?
    - timschmidt 1y ago
      No. SpaceX's Merlin engines use a single https://en.wikipedia.org/wiki/Pintle_injector https://en.wikipedia.org/wiki/Pintle_injector which has excellent throttling capabilities.
    - Tuna-Fish 1y ago
      They do throttle, and quite low compared to other comparable engines, but they still cannot throttle an engine below 1 TWR when the stage is near empty. Meaning that they cannot hover a stage, either the engine is on and the stage is accelerating upwards, or it's off and it's accelerating downwards. (And you cannot rapidly turn engines on and off.) So they need to "hoverslam", that is, arrive at the landing pad rapidly decelerating so that their altitude hits zero just as their speed hits zero. This was thought to be very hard, but I don't think SpaceX has lost a stage due to estimation failure there. It helps that there is significant throttle range and fairly rapid throttle response on the engines, so they can have some slack. (Plan to decelerate at 2.5g for the last ~20s or so, with the ability to do anything between ~1.5g to 4g, so you can adjust throttle based on measured landing speed.) Their Superheavy has more engines, allowing them to bring the TWR below 1, enabling hovering.
starik36 1y ago
I don't know about easy. Today we have exactly 1 proven reusable orbital class family of rockets: Falcon. And even at that Falcon 9 only recovers 1st stage and the fairings. And Falcon Heavy has never recovered the center stage. There might be more in a year or two (New Glenn, Neutron, Starship, a Chinese one), but for now, I would call it extremely difficult, not easy.
didibus 1y ago
Someone proved that there is market demand which could make it profitable. In the past, there was not much reasons to go into space, commercially, so who would have paid for it? But today there are many more use-cases for sending things to space that are willing to pay for the service.
jessriedel 1y ago
The premise of this question is wrong, and it's super disappointing that everyone is giving answers as if it's correct. The Honda test rocket only went to an altitude of 300 meters. It's been possible to propulsively land rockets from such low altitudes for decades, e.g., McDonnell Douglas DC-X test in 1996. (And ofc, if you're just talking about re-use for any landing method, the space shuttle first reused the solid rockets and the orbiter in 1981.) Reusable, propulsively landed stages for rockets capable of putting payloads into Earth orbit is stupendously harder. The speeds involved are like 10-100x higher than these little hops. The first stages of Falcon 9 and Starship are still the only rockets that have achieved that. Electron has only re-used a single engine.
Avshalom 1y ago
It's always been easy. People just didn't think it made much sense. The thing about reusability is that it seriously cuts down on your payload. I mean for/example the Apollo lander was a tail landing rocket and lunar landing is way fucking harder because a thick atmosphere gives you some room for error.
numpad0 1y ago
It's not hard-hard to build recoverable rockets, but it's hard to make money launching reusable rockets that goes to space. This one is not going to space, not making money, and not clear if it's reusable. Most launch suppliers just make rockets single-use and write it off because it's not like you're launching weekly. Who knows how much it costs in labor and parts to refurbish landed rockets, it's probably cheaper to just keep making new ones. ^ you know what to say in response to this; we're all in the process of finding out which one is more correct.
- SoftTalker 1y ago
  What is the point of making a recoverable rocket if not to reuse it (or at least reuse substantial components)?
  - numpad0 1y ago
    Exactly why the rest of the world isn't jumping into it. $THEY are still skeptical of airplane style rapid reuse, so much so that vehicles with zero reusability like Mitsubishi H3 are still being designed from clean sheet.
carabiner 1y ago
It is not easy. ESA and China are still working to catch up to Grasshopper. Other US companies like ULA, Astra, RocketLab are still struggling.
RataNova 1y ago
I think it's not easy per se, but way more achievable for a well-funded team than it was 20 years ago

Question why is it so easy today to build reusable rockets? Is it because the onboard cpu speed of the chips can solve more granular control problems with low latency?

kurthr 1y ago

Proof of concept. It's a lot easier to do something, if you know it can be done.

mempko 1y ago
I mean, SpaceX also knew it could be done since reusable rocket tests happened in the 90s.
- kurthr 1y ago
  Don't you mean the SpaceShuttle in the 80s? or Delta Clipper which didn't reach orbit? Really, what SpaceX did was radically different from the tests in the 90s from the rockets, to the controls, to the reusability goals. Otherwise they wouldn't have built Grasshopper. Now NewGlen is kinda a knockoff of Delta Clipper, but that's a different beast.
- mensetmanusman 1y ago
  And physics, nothing prevents the goal beyond execution.
- hwillis 1y ago
  The DC-X was 9.1 tonnes empty and 19 tonnes full- meaning landing thrust was ~half of takeoff thrust. The Falcon 9 was 400 tonnes full and 26 tonnes empty, so takeoff thrust was >20x higher than landing thrust. That's a huge engineering difference, roughly like the difference between a car and a helicopter. The Falcon 9 was also 4x taller, meaning 16x more force to correct a lean. A little burp would send the rocket right back up in the air.
benjiro 1y ago
Its more about money. If you know that something can be done, and there is a potential market for such a project, it then becomes easier to get the funding. Chicken or the egg... One thing we also need to point out, is that SpaceX uses like 80% of their yearly launches, for their own communication / sat service. This gave a incentive for that investment. Is the same reason why, despite SpaceX throwing those things up constantly, there really is a big lag of competitors with reusable rockets. Its not that they where / not able to quickly get the same tech going. They simply have less market, vs what SpaceX does non-stop. So the investments are less, what in time means less fast development. SpaceX is a bit of a strange company, partially because they used a lot of the public funds to just throw shit at the wall, and see what sticks. This resulted in them caring less if a few rockets blew up, as long as they got the data for the next one with less flaws. It becomes harder when there is more oversight of that money, or risk averse investors. Then you really want to be sure that thing goes up and come back down into one piece from the first go. A lot of projects funding are heavily based upon the first or second try of something, and then (sometimes unwisely) funding is pulled if it was not a perfect success story.
- kurthr 1y ago
  I agree, a lot is about money, but it's not like Honda is raising external funds. Getting management to agree to do anything pretty much requires guaranteed success in large organizations.
- PaulHoule 1y ago
  Even before SpaceX started launching their own satellites in huge numbers they had a business model where they were selling the launch, not the rocket, and selling it at a fixed price, so if some small refinement saved them 5% on launch costs it went to their pockets so they had an incentive to make those small refinements. Dragon 9 was based on conservative and boring technology but it was cost optimized before it was reusable, then reusability crushed the competition. For that matter, Starship is boring. "Throw at the wall and see what sticks" isn't "trying a bunch of crazy stuff" but trying a bunch of low and medium risk things. For instance, development of the Space Shuttle thermal tiles was outrageously expensive and resulted in a system that was outrageously expensive to maintain. They couldn't change it because lives were at stake. With Starship they can build a thermal protection system which is 90% adequate and make little changes that get it up to 100% adequate and then look at optimizing weight, speed of reuse and all that. If some of them burn up it is just money since there won't be astronauts riding it until it is perfected.
PaulHoule 1y ago
Also psychology and politics kept people from following the easy path. The Space Shuttle was wrong in so many ways, not least that it was a "pickup truck" as opposed to a dedicated manned vehicle (with appropriate safety features) or a dedicated cargo vehicle. Because they couldn't do unmanned tests they were stuck with the barely reusable thermal tiles and couldn't replace them with something easier to reuse (or safer!) Attempts at second generation reusable vehicles failed because rather than "solving reuse" they were all about single-stage to orbit (SSTO) [2] and aerospike engines and exotic composite materials that burned up the money/complexity/risk/technology budgets. There was a report that came out towards the end of the SDI [3] phase that pointed out the path that SpaceX followed with Dragon 9 where you could make rather ordinary rockets and reuse the first stage but expend the second because the first stage is most of the expense. They thought psychology and politics would preclude that and that people would be seduced by SSTO, aerospikes, composites, etc. Funny though out of all the design studies NASA did for the Shuttle and for heavy lift vehicles inspired by the O'Neill colony idea, there was a sketch of a "fly back booster" based on the Saturn V that would have basically been "Super Heavy" that was considered in 1979 that, retrospectively, could have given us Starship by 1990 or so. But no, we were committed to the Space Shuttle because boy the Soviet Union was intimidated by our willingness and ability to spend on senseless boondoggles! [1] The first few times the shuttle went up they were afraid the tiles would get damaged and something like the Columbia accident would happen, they made some minor changes to get them to stick better and stopped worrying, at least in public. It took 100 launches for a failure mode than affects 1% of launches to actually happen. [2] https://en.wikipedia.org/wiki/Single-stage-to-orbit https://en.wikipedia.org/wiki/Single-stage-to-orbit [3] https://en.wikipedia.org/wiki/Strategic_Defense_Initiative https://en.wikipedia.org/wiki/Strategic_Defense_Initiative (which would have required much cheaper launch)
- EvanAnderson 1y ago
  > The Space Shuttle was wrong in so many ways, not least that it was a "pickup truck" as opposed to a dedicated manned vehicle (with appropriate safety features) or a dedicated cargo vehicle. I wonder what the STS system would have been like if the DoD's cross-range requirement hadn't been imposed.
bookofjoe 1y ago
See, for example: 4-minute mile
- LeifCarrotson 1y ago
  I don't know how relevant that is. That's something that can be done by an individual, training for something slightly slower than 4 minutes and pushing through to achieve a time that onlookers might not have expected. The real friction in building a reusable rocket isn't the engineering, it's setting "let's build a reusable rocket" as a design goal, and getting a whole bunch of engineers and a whole bunch of dollars to start on that goal. You have to start with a whiteboard sketch and board-room presentation that shows it's achievable, and then send the engineers out to refine the sketch into something worth funding, and then work for months or years to build a rocket that would be a disaster if it's not achievable.
  - bookofjoe 1y ago
    >Proof of concept. It's a lot easier to do something, if you know it can be done. This. What I wanted to emphasize was how, after Bannister finally broke through the 4-minute barrier, many others did it soon after: 3 more in 1954; 4 in 1955; 3 in 1956; 5 in 1957; 4 in 1958. List: https://imgur.com/a/UadE3xa https://imgur.com/a/UadE3xa

odo1242 1y ago

I mean, it's mostly that we've decided to try to do it nowadays. Problems tend to get easier when we put hundreds of thousands of hours of work into them. It wasn't in the scope of the original rocket projects because if it was, we probably would never have launched them.

yieldcrv 1y ago

Because there’s a bigger market for space cargo I wouldn’t say anything has fundamentally changed in the rocket coordination tech itself, just the private sector being able to rationalize the cost of the trials with ROI

xeromal 1y ago

SpaceX showed it was possible and also a crappy place to work means those knowledgeable people go work elsewhere for less work and more money. inb4 blue origin / DC-X did it first

bryanlarsen 1y ago
Actually, the DC-X did it first, in 1993. The DC-X was the first vertical rocket landing, Blue Origin was the first vertical landing of a rocket that went to space, and SpaceX was the first vertical landing of an orbital rocket. This Honda landing neither went to space nor was orbital, so it was a similar test to the DC-X test.
- LorenDB 1y ago
  Actually, retropeopulsive landing was demonstrated during the Apollo program, both on the moon with the LM and with LM trainers on the earth. Those systems were human controlled, of course.
mensetmanusman 1y ago
Crappy for 10% amazing for 90%, somewhat better than the 80/20 70/30 seen by most F500s.
- MattRix 1y ago
  I imagine they mean crappy as in really poor work life balance.

treis 1y ago

This doesn't feel like that much of an accomplishment relatively speaking. It's a smallish rocket that went up and down. Very far away from landing something 100 times heavier from orbit.

lupusreal 1y ago
Nobody is propulsively landing anything from orbit yet. (Dragon is supposedly capable of it, as a backup if the chutes fail, but has never done so.)
- xixixao 1y ago
  Starship is already pretty much there (almost-orbit and water splash)
  - lupusreal 1y ago
    They've had three failures since those earlier successes, and while I expect they'll get it eventually I wouldn't count them as doing it yet. Besides SpaceX, its also being worked on by Rocket Lab, Stoke, maybe Blue Origin, and too many Chinese companies to count.
- deleted 1y ago
  [deleted]

FuriouslyAdrift 1y ago

They've been working on this (in cooperation with JAXA (Japan's NASA)) since 2021.

rvnx 1y ago

We now have realistic simulators like: http://orbit.medphys.ucl.ac.uk/ http://orbit.medphys.ucl.ac.uk/ -> (it's free and open-source: https://github.com/orbitersim/orbiter https://github.com/orbitersim/orbiter ) so now the main problem is building the hardware, there are a lot of solutions for the software part. Before there were no general-purpose simulators, and barely usable computers (2 MHz computer with 2 KB of memory...), so all you could do was hardcoding the path and use rather constrained algorithms.

roshdodd 1y ago
I don't think this was the cause. Advanced simulation capabilities have existed for many decades in the industry. Many if not most of those tools are not publicly available. I think there is also a distinction to be made between offline (engineering) and onboard computing resources. While onboard computers have been constrained in the past, control algorithms are typically simple to implement. Most of the heavy lifting (design & optimization of algorithms) is done in the R&D phase using HPC equipment.
- nine_k 1y ago
  You can now buy vastly more computing power and do fancy fluid dynmaics, etc thanks to GPUs. 20 years ago it was much more expensive to procure, and much harder to find expertise. 30 years ago, I suppose, the field was even less mature, and limited to the few HPC installations and in-house bespoke software. Mass-produced hardware drove prices down, and availability way up, in many industries: motors, analog electronics, computers, solar panels, lithium batteries, various sensors, etc. Maybe reusable rockets, enabled by all that, are going to follow a similar trajectory as air transportation.
  - chasil 1y ago
    If we are going to be specific, 64-bit ARM (in the form of AArch64) arrived in 2011. It would seem to me that Intel and AMD were not friendly to custom designs at that time, and MIPS was not significantly evolving. A fast, low-power CPU that can access more than 4gb and is friendly to customization seems to me to be a recent development.

rsynnott 1y ago

I mean, it's been around as a concept since at least the 50s, but there was quite a lot of scepticism that it was worth the cost (this would only have been reinforced by the Shuttle, whose 'reusable' engines were a bit of a disaster)

advisedwang 1y ago

I don't know the answer, but some possibilities beyond CPU capabilities include: * Better motors for gimballing * Launch-thrust engines that throttle down low enough and preciesly enough for landing * Better materials to handle stress for flip over manover etc without added weight * More accurate position sensors * Better understanding and simulation of aerodynamics to develop body shape and write control algorithms.

hwillis 1y ago
Electrical engineer: motors and sensors are not really any better- motors have gotten more efficient and sensors have gotten cheaper, but gold standard sensors like ring laser gyroscopes have existed since the 60s. > Launch-thrust engines that throttle down low enough and preciesly enough for landing In large part this is due to improved simulation- spaceX made their own software: https://www.youtube.com/watch?v=ozrvfRHvYHA&t=119s https://www.youtube.com/watch?v=ozrvfRHvYHA&t=119s Experimentation was also a large factor- pintle injectors have been around for a long time, but were not used in production rockets until SpaceX (who moved from a single pintle to an annular ring). Pintle injectors are very good for throttling. > Better materials to handle stress for flip over manover etc without added weight We're still using the same materials- good ol inconel and aluminum. However 3d printing has made a pretty big difference in engines. More rockets use carbon fiber, but that isn't new exactly and the main parts are still the same variety of aluminum etc. Titanium has become more common, but is still pretty specialized- the increased availability was probably the biggest factor but improved cutting toolings (alloys and coatings) and tools (bigger, faster, less vibration) have also made a big difference.

roshdodd 1y ago

As someone who actively works in the field, it was a culmination of: - Advances in rocket engine design & tech to enable deep throttling - Control algorithms for propulsive landing maturing (Google "Lars Blackmore", "GFOLD", "Mars Landing", and work through the references) - Forward thinking and risk-taking by SpaceX to further develop tech demonstrated by earlier efforts (DC-X, Mars Landing, etc.) Modern simulation and sensor capabilities helped, but were not the major enabling factors.

bumby 1y ago
Can you elaborate on the advances in deep throttling?
- 93po 1y ago
  Also didnt spacex do reuse without throttling and only having on/off?
  - timschmidt 1y ago
    No. SpaceX's Merlin engines use a single https://en.wikipedia.org/wiki/Pintle_injector https://en.wikipedia.org/wiki/Pintle_injector which has excellent throttling capabilities.
  - Tuna-Fish 1y ago
    They do throttle, and quite low compared to other comparable engines, but they still cannot throttle an engine below 1 TWR when the stage is near empty. Meaning that they cannot hover a stage, either the engine is on and the stage is accelerating upwards, or it's off and it's accelerating downwards. (And you cannot rapidly turn engines on and off.) So they need to "hoverslam", that is, arrive at the landing pad rapidly decelerating so that their altitude hits zero just as their speed hits zero. This was thought to be very hard, but I don't think SpaceX has lost a stage due to estimation failure there. It helps that there is significant throttle range and fairly rapid throttle response on the engines, so they can have some slack. (Plan to decelerate at 2.5g for the last ~20s or so, with the ability to do anything between ~1.5g to 4g, so you can adjust throttle based on measured landing speed.) Their Superheavy has more engines, allowing them to bring the TWR below 1, enabling hovering.

starik36 1y ago

I don't know about easy. Today we have exactly 1 proven reusable orbital class family of rockets: Falcon. And even at that Falcon 9 only recovers 1st stage and the fairings. And Falcon Heavy has never recovered the center stage. There might be more in a year or two (New Glenn, Neutron, Starship, a Chinese one), but for now, I would call it extremely difficult, not easy.

didibus 1y ago

Someone proved that there is market demand which could make it profitable. In the past, there was not much reasons to go into space, commercially, so who would have paid for it? But today there are many more use-cases for sending things to space that are willing to pay for the service.

jessriedel 1y ago

The premise of this question is wrong, and it's super disappointing that everyone is giving answers as if it's correct. The Honda test rocket only went to an altitude of 300 meters. It's been possible to propulsively land rockets from such low altitudes for decades, e.g., McDonnell Douglas DC-X test in 1996. (And ofc, if you're just talking about re-use for any landing method, the space shuttle first reused the solid rockets and the orbiter in 1981.) Reusable, propulsively landed stages for rockets capable of putting payloads into Earth orbit is stupendously harder. The speeds involved are like 10-100x higher than these little hops. The first stages of Falcon 9 and Starship are still the only rockets that have achieved that. Electron has only re-used a single engine.

Avshalom 1y ago

It's always been easy. People just didn't think it made much sense. The thing about reusability is that it seriously cuts down on your payload. I mean for/example the Apollo lander was a tail landing rocket and lunar landing is way fucking harder because a thick atmosphere gives you some room for error.

numpad0 1y ago

It's not hard-hard to build recoverable rockets, but it's hard to make money launching reusable rockets that goes to space. This one is not going to space, not making money, and not clear if it's reusable. Most launch suppliers just make rockets single-use and write it off because it's not like you're launching weekly. Who knows how much it costs in labor and parts to refurbish landed rockets, it's probably cheaper to just keep making new ones. ^ you know what to say in response to this; we're all in the process of finding out which one is more correct.

SoftTalker 1y ago
What is the point of making a recoverable rocket if not to reuse it (or at least reuse substantial components)?
- numpad0 1y ago
  Exactly why the rest of the world isn't jumping into it. $THEY are still skeptical of airplane style rapid reuse, so much so that vehicles with zero reusability like Mitsubishi H3 are still being designed from clean sheet.

carabiner 1y ago

It is not easy. ESA and China are still working to catch up to Grasshopper. Other US companies like ULA, Astra, RocketLab are still struggling.

RataNova 1y ago

I think it's not easy per se, but way more achievable for a well-funded team than it was 20 years ago