7 ms·

The Launch Landscape: Small Rockets

50 points by slyall 5y ago

webmaven 5y ago
Is there a theoretical lower limit to the size of an orbit-capable launch vehicle if the payload size keeps shrinking?
- Sanzig 5y ago
  On earth, about 30 feet in length due to the atmosphere, although I will admit I don't have a firm intuition for why this is the case. [1] https://www.airspacemag.com/space/the-one-pound-problem-718812/ https://www.airspacemag.com/space/the-one-pound-problem-7188...
  - fnord77 5y ago
    > A terrestrial rocket has to push through a plug of air equivalent to a 30-foot column of water, and physics dictates that the smallest vehicle capable of moving all that atmospheric mass without paying a penalty in momentum is about 30 feet long. This doesn't make sense - they're talking about momentum, but then conflating that with a length rather than a mass
    - jjk166 5y ago
      The momentum to length thing comes from Newton's approximation for impact depth, which basically states that the distance a high speed projectile can penetrate something is a function of its density and length. Something like an asteroid or needs a certain minimum length to make it through the atmosphere without slowing down below the speed of sound. It has nothing to do with rockets though, as rockets are not high velocity projectiles - they are powered vehicles and most of the time they are in the atmosphere they're not even going that fast. For space launch this condition would only be relevant if you're being shot out of a massive cannon or something. https://en.wikipedia.org/wiki/Impact_depth https://en.wikipedia.org/wiki/Impact_depth
  - Gravityloss 5y ago
    Excluding the atmosphere, delta vee is exhaust velocity times the logarithm of the mass ratio. The mass of a pressure vessel is proportional to its volume. So if you double the propellant, also tank volume doubles and also tank mass doubles. No clear scale related terms there. Gravity also is not affected by scale, gravity losses are strictly related to mass. But air resistance is different. It is a surface effect and thus related to scale. It's roughly proportional to the frontal area of the rocket. Hence, if you grow a rocket and keep its shape intact, the air resistance grows only as square, but the other factors like mass grow as cube. So bigger rockets have a smaller proportion of their delta vee spent on air resistance losses. That's also why sounding rockets are so skinny. Air resistance dominates there. (They are also accelerating faster since they are rail launched and don't have active gimbal guidance, which makes it even worse) You can think of a medium sized orbital rocket, and then if you shrink it, the only way to keep its payload to total mass rate the same is to keep the air resistance losses same related to the total mass - ie keep its original length and only shrink it sideways.
- jjk166 5y ago
  There isn't really a theoretical minimum size, but with the best chemical propulsion possible you're going to have an initial to final mass ratio of about 5. Now that final mass needs to include the structure of the vehicle, so you can cheat a little bit with staging but you can't make it go to zero. In practice, the smallest orbital launch vehicle ever launched required 2600 kg to launch a 4 kg payload. Turns out that the smaller a rocket is, the less mass efficient it gets.
jpm_sd 5y ago
I'm not sure there is an "oversupply" of small launch, most of these companies haven't yet had a successful launch and probably will run out of money before they do!
LightG 5y ago
It tickles me that even the smallest operator on this list could launch me (in a suitable person-shaped container) into space, and some operators could also even recover me before I hit the ground. Is there a market for this?!
- shadilay 5y ago
  Are you factoring in the weight/complexity of the life support system?
  - LightG 5y ago
    I figured the flight would be short enough to get by with scuba-gear inside a pressurised compartment.
    - shadilay 5y ago
      That sounds like a terrifically bad idea. Temperature/pressure/G loading https://en.wikipedia.org/wiki/Mike_Hughes_(daredevil) https://en.wikipedia.org/wiki/Mike_Hughes_(daredevil)
      - LightG 5y ago
        Hmm, you might have a good point there. I'll double check your calculations - but it looks like it's back to the drawing board for me.
throwaway69123 5y ago
I have no expertise in rockets but I have often wondered why for ultra small pay loads you couldn’t use a balloon stage and then a rocket stage
- danielvf 5y ago
  Almost all the energy/velocity needed for orbiting is "sideways" to the earth. Imagine needed to throw a baseball fast enough that it goes fast enough that the barely visible curve of earth falling away the same as the dropping of the baseball from gravity. The ISS moves around the Earth at approximatle 28,800 kilometers per hour (17,900 mph). For comparison, a bullet fired in a vacuum at only 2,000 kilometers per hour will reach about 15km up, or a reasonable ballon launch height.
  - NortySpock 5y ago
    I have started phrasing Earth's orbital velocity as "Mach 25" to give people a sense of scale. For some reference, "hypersonic" is defined as "greater than Mach 5", and Google says the fastest rifle muzzle velocity is under Mach 4.
    - SiempreViernes 5y ago
      Yeah, hypersonic has really gotten the buzzword treatment these last few years.
      - SonicScrub 5y ago
        Just to be clear, space vehicles are not "hypersonic". They travel these speeds outside of substantial atmosphere, where the speed of sound is undefined. Mach number is relative to local air conditions, ergo their Mach number isn't 25. It's undefined. Mach Number is a meaningless quantity. It's not accurate to say that a space vehicle travels Mach 25, only that it's speed is 25 times higher than the speed of sound at sea-level conditions. Saying this can be a useful reference to give context to the insane speed of orbital vehicles (as was done by the commenter above you). I say all this to give context about the surge in hypersonic research in recent years as being something distinctly different than achievements made in space-vehicles. It's not really accurate to say it's been given the "buzzword" treatment simply because things in space already move so fast. There's a distinct advantage (particularly for military objectives) to flying above Mach 5 in the atmosphere.
neartheplain 5y ago
In the even-smaller rockets category, Copenhagen Suborbitals is still kicking, having survived its founder's murder conviction: https://copenhagensuborbitals.com/ https://copenhagensuborbitals.com/ https://en.wikipedia.org/wiki/Copenhagen_Suborbitals#History https://en.wikipedia.org/wiki/Copenhagen_Suborbitals#History
- Bronze_Colossus 5y ago
  Should clarify that Madsen was kicked out of Copenhagen Suborbitals years before he murdered someone.
baybal2 5y ago
Turkish Roketsan has a plan to offer launch on its sounding rockets with 2nd, and 3rd stages added. 1st stage test went 9 months ago.
SonicScrub 5y ago
Related to this topic: a new small launch company C6 Launch systems just performed an engine integration test with engine start-up Ursa Major. https://www.linkedin.com/company/c6-launch-systems/?originalSubdomain=ca https://www.linkedin.com/company/c6-launch-systems/?original... It's been interesting to see the number of small-launch companies increase over the past few years. I'm not sure if the market will support the number of companies currently vying for a slice . I'm curious to see which ones are able to make it and which ones won't.
gremlinsinc 5y ago
Here's an idea...maybe companies could play "nice" together...and have like a rocket "meeting place" where rockets basically go after they deliver payload. Then spacex's BFR goes up, some robot collects them all inside the ship and loads them...brings them home.... saving lots of money for everyone and spacex maybe pockets a retrieval fee per rocket based on weight or something.... This is assuming small rockets are also expensive and could save money if they could reuse them.
- natosaichek 5y ago
  Most of the rockets listed are 2-stage rockets. The first stage never makes it to orbit - it just falls back down to earth after dropping off the second stage. The second stage often does make it to orbit, where it deploys the payload and then usually becomes orbital debris. A few upper stages (falcon 9, for example) do a small engine burn to reenter the atmosphere where they burn up. Collecting upper stages would be... hard. Every rocket is on a different trajectory. Making some vessel that could 'collect' them would have to visit every launch trajectory that they'd each taken, which is a lot of orbital maneuvering and coordination. Then the problem of docking and collecting the stages and packaging them for reentry would be a whole series of ridiculously tough engineering challenges. The upper stage is much smaller than the first stage, so it's usually significantly cheaper than the first stage. Basically, recovery of the upper stage is much harder than recovery of the first stage and has less upside.
h2odragon 5y ago
Still no backers for my "Big Arse Slingshot to Orbit" idea, alas. We might just be getting to the point where useful functions can be packaged small and tough enough to survive a cannon type launch. Artillery to orbit might be made to work today. https://en.wikipedia.org/wiki/Space_gun https://en.wikipedia.org/wiki/Space_gun
- ivorbach 5y ago
  There's actually a well-funded, VC backed startup pursuing this very strategy if you're interested in checking them out! https://techcrunch.com/2020/01/16/spinlaunch-spins-up-a-35m-round-to-continue-building-its-space-catapult/ https://techcrunch.com/2020/01/16/spinlaunch-spins-up-a-35m-...
  - SonicScrub 5y ago
    I'm not convinced that Spin-Launch is anything but vapour-ware. At risk of sounding like an arm-chair engineer, the G-forces experienced by the payload during it's rotational-phase must be astronomical. Not to mention the aero and thermal loads of slamming into the thick lower atmosphere at a substantial fraction of orbital velocity. The aerospace startup industry is no stranger to dumb ideas getting inexplicably large amounts of start-up capital, so capital itself isn't a reliable measure of their engineering expertise. We shall see though. EDIT: g-force calculation in a centrifuge is velocity^2 / radius. A 1st stage probably needs at least 4 km/s. A 10 km radius centrifuge yields a gigantic 1600 gs at that speed. So they're either building a centrifuge the size of a medium sized city, or their stage 1 speed is so slow that why bother with the added engineering complexity of this portion? This is without even considering the thermal and aero problem that emerges with high-speed flight at sea-level upon exiting the centrifuge. I think I'd keep my wallet closed on this one if I was an investor. Is there something I'm missing somehow here?
    - ivorbach 5y ago
      I agree, it's hard to imagine a payload that could withstand the g-forces required to reach space through a centrifuge launch. I think what interests investors is that in the low likelihood they succeed, they could create an order-of-magnitude reduction in launch costs. Some investors seem to have decided that was worth the bet
brandmeyer 5y ago
The reason these guys are in deep trouble is SpaceX. Current pricing is 1 megabuck per 200 kg for small customers (5 kUSD/kg). That's today's price on a rocket with a substantial launch history of success. Third-party observers estimate that SpaceX's own cost is more like 1 kUSD/kg. So, they've got some room to move their prices if the competition gets close. But the competition isn't even remotely close, at 2-3x the price. Astra's aspirational goal is 5 kUSD/kg, and 12.5 kUSD/kg initially. Alpha: 15 kUSD/kg. Vega: 15 kUSD/kg. They are default-dead.
- Sanzig 5y ago
  I think there's room for both. Going on a $ per kg metric is drastically oversimplifying the other factors that go into launch vehicle selection. SpaceX rideshare is great if you have a mission that you want to launch to a popular orbit or an orbit near enough to a popular one that you can close the gap with on-orbit propulsion. However, the cost savings come with disadvantages. You don't get to pick your launch date, and if you miss your launch, SpaceX isn't waiting for you. It could be a long time before the next rideshare that's going to the orbit you want is available. If you want an oddball orbit, or you want the flexibility to set your own launch date and maybe delay it if you have program delays, the smallsat launchers could make a lot of sense even if they are 5-10x the cost on a per kilogram basis. Space missions are really expensive, and it's not the launch that's the driver of that anymore - it's the engineering, customization, and other overhead involved with developing and operating a spacecraft. You can (and should) use off-the-shelf hardware such as a finished satellite bus from somebody like SSTL or Blue Canyon, but you still have to develop the concept of operations, requirements, payload, operations plan, operations infrastructure, and staff the operating team (which is often a 24/7 endeavour, or at least an 8/7 endeavour with on-call night staff). To put it another way: if your total lifetime mission cost is going to be $50M-75M (not an unrealistic figure for a novel SmallSat mission) and you're looking at $1M for SpaceX versus $7M for RocketLab (to use the numbers from the article), the answer may not be immediately obvious. There may be serious advantages to a dedicated launch at the cost of growing the program budget by about 10%. It's totally situational.
  - brandmeyer 5y ago
ivorbach 5y ago
Author here! So exciting to see my newsletter on HN! Thank you for taking the time to read, I really appreciate it. Happy to answer any questions or respond to comments as well!

50 points by slyall 5y ago

webmaven 5y ago

Is there a theoretical lower limit to the size of an orbit-capable launch vehicle if the payload size keeps shrinking?

Sanzig 5y ago
On earth, about 30 feet in length due to the atmosphere, although I will admit I don't have a firm intuition for why this is the case. [1] https://www.airspacemag.com/space/the-one-pound-problem-718812/ https://www.airspacemag.com/space/the-one-pound-problem-7188...
- fnord77 5y ago
  > A terrestrial rocket has to push through a plug of air equivalent to a 30-foot column of water, and physics dictates that the smallest vehicle capable of moving all that atmospheric mass without paying a penalty in momentum is about 30 feet long. This doesn't make sense - they're talking about momentum, but then conflating that with a length rather than a mass
  - jjk166 5y ago
    The momentum to length thing comes from Newton's approximation for impact depth, which basically states that the distance a high speed projectile can penetrate something is a function of its density and length. Something like an asteroid or needs a certain minimum length to make it through the atmosphere without slowing down below the speed of sound. It has nothing to do with rockets though, as rockets are not high velocity projectiles - they are powered vehicles and most of the time they are in the atmosphere they're not even going that fast. For space launch this condition would only be relevant if you're being shot out of a massive cannon or something. https://en.wikipedia.org/wiki/Impact_depth https://en.wikipedia.org/wiki/Impact_depth
- Gravityloss 5y ago
  Excluding the atmosphere, delta vee is exhaust velocity times the logarithm of the mass ratio. The mass of a pressure vessel is proportional to its volume. So if you double the propellant, also tank volume doubles and also tank mass doubles. No clear scale related terms there. Gravity also is not affected by scale, gravity losses are strictly related to mass. But air resistance is different. It is a surface effect and thus related to scale. It's roughly proportional to the frontal area of the rocket. Hence, if you grow a rocket and keep its shape intact, the air resistance grows only as square, but the other factors like mass grow as cube. So bigger rockets have a smaller proportion of their delta vee spent on air resistance losses. That's also why sounding rockets are so skinny. Air resistance dominates there. (They are also accelerating faster since they are rail launched and don't have active gimbal guidance, which makes it even worse) You can think of a medium sized orbital rocket, and then if you shrink it, the only way to keep its payload to total mass rate the same is to keep the air resistance losses same related to the total mass - ie keep its original length and only shrink it sideways.
jjk166 5y ago
There isn't really a theoretical minimum size, but with the best chemical propulsion possible you're going to have an initial to final mass ratio of about 5. Now that final mass needs to include the structure of the vehicle, so you can cheat a little bit with staging but you can't make it go to zero. In practice, the smallest orbital launch vehicle ever launched required 2600 kg to launch a 4 kg payload. Turns out that the smaller a rocket is, the less mass efficient it gets.

jpm_sd 5y ago

I'm not sure there is an "oversupply" of small launch, most of these companies haven't yet had a successful launch and probably will run out of money before they do!

LightG 5y ago

It tickles me that even the smallest operator on this list could launch me (in a suitable person-shaped container) into space, and some operators could also even recover me before I hit the ground. Is there a market for this?!

shadilay 5y ago
Are you factoring in the weight/complexity of the life support system?
- LightG 5y ago
  I figured the flight would be short enough to get by with scuba-gear inside a pressurised compartment.
  - shadilay 5y ago
    That sounds like a terrifically bad idea. Temperature/pressure/G loading https://en.wikipedia.org/wiki/Mike_Hughes_(daredevil) https://en.wikipedia.org/wiki/Mike_Hughes_(daredevil)
    - LightG 5y ago
      Hmm, you might have a good point there. I'll double check your calculations - but it looks like it's back to the drawing board for me.

throwaway69123 5y ago

I have no expertise in rockets but I have often wondered why for ultra small pay loads you couldn’t use a balloon stage and then a rocket stage

danielvf 5y ago
Almost all the energy/velocity needed for orbiting is "sideways" to the earth. Imagine needed to throw a baseball fast enough that it goes fast enough that the barely visible curve of earth falling away the same as the dropping of the baseball from gravity. The ISS moves around the Earth at approximatle 28,800 kilometers per hour (17,900 mph). For comparison, a bullet fired in a vacuum at only 2,000 kilometers per hour will reach about 15km up, or a reasonable ballon launch height.
- NortySpock 5y ago
  I have started phrasing Earth's orbital velocity as "Mach 25" to give people a sense of scale. For some reference, "hypersonic" is defined as "greater than Mach 5", and Google says the fastest rifle muzzle velocity is under Mach 4.
  - SiempreViernes 5y ago
    Yeah, hypersonic has really gotten the buzzword treatment these last few years.
    - SonicScrub 5y ago
      Just to be clear, space vehicles are not "hypersonic". They travel these speeds outside of substantial atmosphere, where the speed of sound is undefined. Mach number is relative to local air conditions, ergo their Mach number isn't 25. It's undefined. Mach Number is a meaningless quantity. It's not accurate to say that a space vehicle travels Mach 25, only that it's speed is 25 times higher than the speed of sound at sea-level conditions. Saying this can be a useful reference to give context to the insane speed of orbital vehicles (as was done by the commenter above you). I say all this to give context about the surge in hypersonic research in recent years as being something distinctly different than achievements made in space-vehicles. It's not really accurate to say it's been given the "buzzword" treatment simply because things in space already move so fast. There's a distinct advantage (particularly for military objectives) to flying above Mach 5 in the atmosphere.

neartheplain 5y ago

In the even-smaller rockets category, Copenhagen Suborbitals is still kicking, having survived its founder's murder conviction: https://copenhagensuborbitals.com/ https://copenhagensuborbitals.com/ https://en.wikipedia.org/wiki/Copenhagen_Suborbitals#History https://en.wikipedia.org/wiki/Copenhagen_Suborbitals#History

Bronze_Colossus 5y ago
Should clarify that Madsen was kicked out of Copenhagen Suborbitals years before he murdered someone.

baybal2 5y ago

Turkish Roketsan has a plan to offer launch on its sounding rockets with 2nd, and 3rd stages added. 1st stage test went 9 months ago.

SonicScrub 5y ago

Related to this topic: a new small launch company C6 Launch systems just performed an engine integration test with engine start-up Ursa Major. https://www.linkedin.com/company/c6-launch-systems/?originalSubdomain=ca https://www.linkedin.com/company/c6-launch-systems/?original... It's been interesting to see the number of small-launch companies increase over the past few years. I'm not sure if the market will support the number of companies currently vying for a slice . I'm curious to see which ones are able to make it and which ones won't.

gremlinsinc 5y ago

Here's an idea...maybe companies could play "nice" together...and have like a rocket "meeting place" where rockets basically go after they deliver payload. Then spacex's BFR goes up, some robot collects them all inside the ship and loads them...brings them home.... saving lots of money for everyone and spacex maybe pockets a retrieval fee per rocket based on weight or something.... This is assuming small rockets are also expensive and could save money if they could reuse them.

natosaichek 5y ago
Most of the rockets listed are 2-stage rockets. The first stage never makes it to orbit - it just falls back down to earth after dropping off the second stage. The second stage often does make it to orbit, where it deploys the payload and then usually becomes orbital debris. A few upper stages (falcon 9, for example) do a small engine burn to reenter the atmosphere where they burn up. Collecting upper stages would be... hard. Every rocket is on a different trajectory. Making some vessel that could 'collect' them would have to visit every launch trajectory that they'd each taken, which is a lot of orbital maneuvering and coordination. Then the problem of docking and collecting the stages and packaging them for reentry would be a whole series of ridiculously tough engineering challenges. The upper stage is much smaller than the first stage, so it's usually significantly cheaper than the first stage. Basically, recovery of the upper stage is much harder than recovery of the first stage and has less upside.

h2odragon 5y ago

Still no backers for my "Big Arse Slingshot to Orbit" idea, alas. We might just be getting to the point where useful functions can be packaged small and tough enough to survive a cannon type launch. Artillery to orbit might be made to work today. https://en.wikipedia.org/wiki/Space_gun https://en.wikipedia.org/wiki/Space_gun

ivorbach 5y ago
There's actually a well-funded, VC backed startup pursuing this very strategy if you're interested in checking them out! https://techcrunch.com/2020/01/16/spinlaunch-spins-up-a-35m-round-to-continue-building-its-space-catapult/ https://techcrunch.com/2020/01/16/spinlaunch-spins-up-a-35m-...
- SonicScrub 5y ago
  I'm not convinced that Spin-Launch is anything but vapour-ware. At risk of sounding like an arm-chair engineer, the G-forces experienced by the payload during it's rotational-phase must be astronomical. Not to mention the aero and thermal loads of slamming into the thick lower atmosphere at a substantial fraction of orbital velocity. The aerospace startup industry is no stranger to dumb ideas getting inexplicably large amounts of start-up capital, so capital itself isn't a reliable measure of their engineering expertise. We shall see though. EDIT: g-force calculation in a centrifuge is velocity^2 / radius. A 1st stage probably needs at least 4 km/s. A 10 km radius centrifuge yields a gigantic 1600 gs at that speed. So they're either building a centrifuge the size of a medium sized city, or their stage 1 speed is so slow that why bother with the added engineering complexity of this portion? This is without even considering the thermal and aero problem that emerges with high-speed flight at sea-level upon exiting the centrifuge. I think I'd keep my wallet closed on this one if I was an investor. Is there something I'm missing somehow here?
  - ivorbach 5y ago
    I agree, it's hard to imagine a payload that could withstand the g-forces required to reach space through a centrifuge launch. I think what interests investors is that in the low likelihood they succeed, they could create an order-of-magnitude reduction in launch costs. Some investors seem to have decided that was worth the bet

brandmeyer 5y ago

The reason these guys are in deep trouble is SpaceX. Current pricing is 1 megabuck per 200 kg for small customers (5 kUSD/kg). That's today's price on a rocket with a substantial launch history of success. Third-party observers estimate that SpaceX's own cost is more like 1 kUSD/kg. So, they've got some room to move their prices if the competition gets close. But the competition isn't even remotely close, at 2-3x the price. Astra's aspirational goal is 5 kUSD/kg, and 12.5 kUSD/kg initially. Alpha: 15 kUSD/kg. Vega: 15 kUSD/kg. They are default-dead.

Sanzig 5y ago
I think there's room for both. Going on a $ per kg metric is drastically oversimplifying the other factors that go into launch vehicle selection. SpaceX rideshare is great if you have a mission that you want to launch to a popular orbit or an orbit near enough to a popular one that you can close the gap with on-orbit propulsion. However, the cost savings come with disadvantages. You don't get to pick your launch date, and if you miss your launch, SpaceX isn't waiting for you. It could be a long time before the next rideshare that's going to the orbit you want is available. If you want an oddball orbit, or you want the flexibility to set your own launch date and maybe delay it if you have program delays, the smallsat launchers could make a lot of sense even if they are 5-10x the cost on a per kilogram basis. Space missions are really expensive, and it's not the launch that's the driver of that anymore - it's the engineering, customization, and other overhead involved with developing and operating a spacecraft. You can (and should) use off-the-shelf hardware such as a finished satellite bus from somebody like SSTL or Blue Canyon, but you still have to develop the concept of operations, requirements, payload, operations plan, operations infrastructure, and staff the operating team (which is often a 24/7 endeavour, or at least an 8/7 endeavour with on-call night staff). To put it another way: if your total lifetime mission cost is going to be $50M-75M (not an unrealistic figure for a novel SmallSat mission) and you're looking at $1M for SpaceX versus $7M for RocketLab (to use the numbers from the article), the answer may not be immediately obvious. There may be serious advantages to a dedicated launch at the cost of growing the program budget by about 10%. It's totally situational.
- brandmeyer 5y ago

ivorbach 5y ago

Author here! So exciting to see my newsletter on HN! Thank you for taking the time to read, I really appreciate it. Happy to answer any questions or respond to comments as well!