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The first on-orbit fuel depot has been deployed
- phreeza 5y agoFrom my understanding of orbital dynamics, this will only be useful to spacecraft already in a precisely matched orbit. So it's not useful to think of this as an orbital gas station that spacecraft can just pull up to in order to refuel.
- tectonic 5y agoA larger, non-experimental depot could use electric propulsion to bring itself to satellites that need to be refueled. It's energetically expensive but likely still worth it to extend the life of expensive satellites.
- JumpCrisscross 5y ago> non-experimental depot could use electric propulsion to bring itself to satellites that need to be refueled. It's energetically expensive but likely still worth it to extend the life of expensive satellites. I'd have to do the math, but I'd be curious about the confluence of launch market dynamics that would make pre-launched depots which need to change orbital planes cheaper than depots launched on demand into the right orbit from the start.
- deleted 5y ago[deleted]
- Someone 5y agoI don’t know how the math turns out, either, but because this thing exists, I would guess it’s so much cheaper to launch one huge depot than a hundred smaller ones (reasons could be higher cargo/total weight ratio and/or lower launch overhead) that it compensates for the extra maneuvering. Of course, that’s gambling on those hundred customers to exist, on refueling to be reliable, etc.
- LeifCarrotson 5y agoIt's true that there's no good reason to, say, drop out of geostationary and visit a tanker in LEO. Plane changes are always expensive, altitude changes are what they are, but if your orbit is reasonably compatible it would take a whole lot less delta V to reach a tanker than it would to come back to the planet's surface and re-launch! This depot is in a sun-synchronous orbit. There are a ton of long-term, extremely expensive, Earth-observing satellites between 600 and 800 km with inclinations of 98 degrees in this area. Yes, it's a large volume of space, and yes, it's not like you can just point yourself at another satellite, fire a thruster, and coast over to it, but if you could extend the lifetime of your billion-dollar meteorological satellite for a few million you might want to have this thing fly over to refuel you. I doubt that they'll be moving massive satellites with huge telescopes, radars, communication dishes, and solar arrays to the tanker, rather, they'll fly the tanker to the satellites.
- blach 5y agoThere are also a proliferating number of sun-sync earth observation small sats. These are often from capital/mass/volume limited new space companies. Lowering their initial launch mass allows them to prove out a business model for a lower cost and then refuel it if it works with future capital. Benchmark's "pay as you go" SaaS-like model is also interesting in the same vein. Edit: correcting a typo
- brandmeyer 5y agoDepends on the fuel, though. Ion thrusters with a solid propellant are becoming popular in the smallsat business.
- JumpCrisscross 5y ago> if you could extend the lifetime of your billion-dollar meteorological satellite for a few million you might want to have this thing fly over to refuel you The pitch for in-orbit refuelling is clear. Less clear is the advantage of a tank in (a close, but wrong) orbit over one on the ground with a launch booked.
- jjk166 5y agoSpacecraft can change their orbits. You don't fly in a straight line to get there but yes, spacecraft can pull up to it. The delta-V for such an orbit change is exceedingly small compared to the cost of a launch.
- kyralis 5y agoThat depends a lot on the change and is not always a true statement.
- jjk166 5y agoWe're specifically referring to small changes here to service satellites in similar orbits. Also, for future reference, please consider this site's guideline "Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith."
- kyralis 5y agoNothing about your post confined the discussion to "similar" orbits; you were in fact responding to a parent describing a need for these to be precisely matched with a negation. While you're correct that there are orbital changes that are cheap, there are many that are not as well, and your statement without that qualification seemed likely to mislead. I wasn't assuming bad faith on your part; I merely believed that your response could be confusing. You might consider that guideline as well.
- jjk166 5y agoThe context of the conversation was that OP's comment was questioning the utility of a depot since they believed spacecraft in similar orbits would not be able to access it, only those that happened to be in precisely aligned orbits could. Interpreting "spacecraft can change their orbits" to be a claim that there are no limitations on the maneuvers a spacecraft can perform is very unreasonable.
- hughes 5y agoDon’t all gas stations require you to precisely match their position and velocity? Like how do you fill up your car without doing this??
- bpye 5y agoI think it might be more reasonable to look at this like air to air refuelling, rather than a petrol station. Either the tanker or the satellite or both must spend a significant amount of fuel to align their orbits and velocities precisely and during that operation they are likely unable to perform anything else.
- jjk166 5y agoIn air to air refueling, both parties are spending incredible amounts of fuel simply holding themselves aloft at cruising speed. Matching alignment is a literal drop in the bucket by comparison. The amount of fuel required to align spacecraft in similar orbits is miniscule compared to the cost of getting fuel into orbit to begin with. You're talking 10s of m/s of delta-V.
- bob1029 5y agoProbably something like this: https://www.youtube.com/watch?v=MKF0KXMha2E https://www.youtube.com/watch?v=MKF0KXMha2E
- ashtonkem 5y agoThere’s a wee bit of difference between matching speed with a gas station and matching speed with a satellite, both in terms of cost and complexity.
- tehbeard 5y agoEhh, it's easy enough to eyeball it. Source: 1000+ hours in KSP :P
- perl4ever 5y agoWell, if everybody did that, they wouldn't have bollards. Or breakaway hoses.
- ChuckMcM 5y agoSort of. The promise of on-orbit refueling is three-fold; First, you can have several tankers in orbit which would allow for an "any day of the week / time of day" launch schedule from Earth for a payload satellite, that then rendezvoused with the tanker in the orbit it found itself in, fueled up, and then did a transition burn to the orbital plane it wanted to be in. That "wins" because the satellite can go up with empty tanks for its orbital maneuvering thrusters, (so more mass can be allocated to the satellite), and the insertion 'tug' can ride along like an unfueled third stage. That eliminates things like "instantaneous launch windows" which keep satellites grounded if everything doesn't come together at exactly the right time. Second, station keeping lifetime can be extended (most common value) and that means you can amortize the satellite's costs over a longer lifetime. Many geosynchronous satellites are "retired" not because they don't work, but because they are about to run out of fuel for keeping their place. If you can refuel a $5M satellite and get another 10 years of life out of it, that is a pretty big deal. And third is the ability to gain fuel post launch as part of a retro-propulsive return profile. The heat shielding of all spacecraft is there because they use "friction" return profiles where they use the atmosphere to slow them down. That is fine but limits the amount of mass you can return because the more mass you displace, the more heat you generate in the return. If you could fill up on fuel on orbit and use that to cancel your orbital velocity, you could do a return to earth that would stay within the heat limits of ordinary steel which would be safer and easier on the spacecraft. ULA was circulating design ideas for a cryogenic fuel depot on orbit that were pretty neat. These are but a few of the limitations that are imposed by having to carry all of the fuel you will ever need on every flight. On orbit refueling would make it much easier to work in space.
- hinkley 5y agoRefueling a satellite in orbit presupposes that the satellite actually made it to orbit. The flip side of amortizing the cost of the satellite over a longer mission is being able to cut your losses a bit in the event that the duration turns out to be 0.
- ChuckMcM 5y agoI don't disagree but I also don't understand what you're trying to say here. All satellites are insured and if they don't make it into orbit the insurance claim reimburses the builder for the cost.
- swader999 5y agoHope it has nice washrooms.
- jeantherapy 5y agowho cares. starship will do this all day long.
- mkr-hn 5y agoA whole Starship to deliver a few tens of pounds of fuel to a satellite seems excessive. The whole thing weighs about as much as a tank of gasoline. A Starship might deploy a hundred of these into different orbits for different refueling tasks.
- ashtonkem 5y agoAh, I used this exact same strategy in KSP. It’s very convenient to lift a huge amount of fuel into space once using a disposable rocket, then top up smaller crafts before heading out of orbit. I assume they won’t be following my “dump extra fuel here before re-entering the atmosphere” strategy though.
- zeusk 5y agoBut why would you dump extra fuel in KSP? couldn't you use it to reduce your surface velocity before atmospheric heating begins? or even use it as thermal mass and do a retrograde burn during landing like Falcon9?
- ashtonkem 5y agoFuel costs money to lift, so by dumping it in the orbital fuel station I can delay an expensive and tedious refueling mission. Deceleration in KSP is easy because the aerodynamic and thermal models are exceptionally forgiving. Assuming you have literally any heat shield, you have to come in at interplanetary transfer speeds with a periapsis below airplane traffic before blowing up due to overheating is a concern. Most players will depend on drag to do the bulk of their deceleration because it’s cheap and easy, and even Falcon 9 style approaches can use parachutes and air brakes to do the heavy lifting. My falcon 9 equivalent rocket just uses a touch of throttle to prevent the landing legs from compressing so much that the rocket bell hits the ground. If I had a bit more clearance I probably wouldn’t need any fuel other than the deceleration burn.
- sandworm101 5y agoIt works in KSP because your a launching from the equator into a zero-incline orbit. In the real world, or modded ksp, the advantages of on-orbit refuel are very difficult to realize. It is basically only practical for geostationary sats. Everything else, everything inclined, would cost more fuel to get to than simply launching a new refueler for every task.
- deleted 5y ago[deleted]
- tjmc 5y agoFirst time I've heard the term "on-orbit" rather than "in-orbit". To my amateur ear it sounds wrong - like a submerged submarine described as "on-sea". There's a good discussion of why it's that way here: https://english.stackexchange.com/questions/5320/in-orbit-vs-on-orbit https://english.stackexchange.com/questions/5320/in-orbit-vs... I like the explanation that something on its way to the correct orbit is "in orbit" and then "on-orbit" when it gets there but is that actually right?
- aaron695 5y agoI think the correct answer is - "On Orbit typically is used to refer to where an action, experiment, or operation is taking place - https://www.theatlantic.com/technology/archive/2014/11/grammar-in-space-are-you-in-orbit-or-on-orbit/381522/ https://www.theatlantic.com/technology/archive/2014/11/gramm... The Atlantic asks NASA and they in turn look at the reports and say the above, but strangely The Atlantic ends up with a English professions definition which is what Stack perhaps repeats. Google seems to agree it's actions if you look at results. It's servicing, rendezvous and capture, refueling, assembly, breakups
- dandelany 5y agoI think of it as “in [any] orbit” vs “on [target] orbit”
- iancmceachern 5y agoIs there some sort of standard refueling port that all these already launched satellites somehow aligned on and is already in use on launched hardware? It seems to me that the most challenging thing about this is that part, how to get the fuel from the tanker to each satellite. Robot arm with a fuel line and standard connector?