r/spaceflight • u/spacedotc0m • 17d ago
Axiom's private space station is coming sooner than we thought
https://www.space.com/space-exploration/private-spaceflight/axioms-private-space-station-is-coming-sooner-than-we-thought11
u/Isnotanumber 17d ago
Semi-random thought. Is it really necessary to send part of this to ISS first? And if so, can its orbit be modified significantly once it becomes a free flying vehicle. As I recall, the orbit for ISS was dictated to give Russians access, and while doable from KSC it kinda sucks. Limits the windows to launch, made the amount payload deliverable a little more limited. At least for Shuttle. Why not just optimize it for launches from the US? Is there a hope of keeping Russia as a partner?
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u/mfb- 17d ago
The payload increase with a lower inclination orbit isn't that large. Launching to the ISS inclination leads to a launch trajectory that follows the US coast, which is nice for launch abort scenarios.
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u/Isnotanumber 17d ago
So were the issues of the orbit ISS ended up in versus Space Station Freedom (which a lot of the US ISS segments were planned for) more a matter of just (frustratingly) updating the weights of everything, to revise where shuttle had to get the pieces of ISS to?
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u/jimhillhouse 16d ago
Doesn’t following the U.S. Easter seaboard, a densely populated area, as opposed to going over the Atlantic when targeting lower inclination orbits of say 28°, present higher risk from a launch abort point of view?
As I recall from an aerospace engineering orbital mechanics lecture at the time ISS’s Harmony module was launched, ISS’s current inclination was solely to accommodate the former Soviet Union’s participation in ISS.
The loss of delta-V from a nearly 24° change in launch azimuth from 28° to 52° isn’t significant, but the impact also and largely hinges on the launch vehicle’s performance, or specific impulse. Here’s an example.
At the equator, the velocity contribution from the earth’s rotation is 464 m/s. The cosine at 28° is 0.88 and that at 52° is 0.62, ~30% less than 28°. So, at 28°, that velocity contribution is ~409.6 m/s; at 52° it’s ~279 m/s.
If we say orbital velocity is 7,800 m/s, at 28° the delta-V required of a launch vehicle is 7,390 m/s and at 52° it is 7,514.4 m/s or so, about an additional 124 m/s more than a vehicle launch at 28° latitude.
Using the Rocket Equation to look at launch vehicle performance at differing launch azimuth and assuming-away its imprecision due to not including various drag components can be useful. For a launch vehicle with a propulsion system performance of 450 s, the mass ratio, which is massWet/massDry, is 5.33 at 28° and 5.49 at 52°, a nearly 30% difference. Higher is worse because the difference between wet and dry mass of a launch vehicle is propellant mass, at least for purposes of calculating performance using the rocket equation.
The payload mass fraction is (MR-1)/MR. At 28° payload mass fraction is 0.812 and at 52° is 0.817. A lower payload mass fraction is better because it means less propellant needed to launch a given payload. So, for a high performance launch vehicle with an ISP of 450s, the change from 28° to 53°represents a 2.77% payload penalty.
For a less performant system like the latest Falcon 9 with an ISP of ~230s, that at 28° the payload fraction is 3.78% and at 52° it’s 3.57%, a difference of 5.35%.
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u/mfb- 15d ago
It doesn't fly over the coast. It flies over the Atlantic, but instead of 2000 km away you might land just 200 km away from the coast. Here is an image.
ISS’s current inclination was solely to accommodate the former Soviet Union’s participation in ISS.
Oh sure, if you don't have a good reason to fly to 52 degrees then you'll always choose a lower inclination.
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u/snoo-boop 14d ago
the launch vehicle’s performance, or specific impulse.
I think performance analysis is more sophisticated these days.
You use 450s ISP as "high performance" ISP, can you let us know which vehicle has that ISP at sea level?
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u/ClearlyFonzii 17d ago
The intention behind this module is to take on payloads from the ISS that NASA and other partners want to keep in orbit and very valuable to NASA and the partners.
Each module has thrusters and propulsion for station keeping and orbital changes if needed. PPTM, as the name implies, has additional prop tanks for orbital chngges if needed.
The final orbit of Axiom station can be changed after separation from ISS.
Source: I'm a design engineer currently working at Axiom on the station.
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u/Martianspirit 17d ago
The ISS inclination gives the ISS access to much of the inhabited area of the Earth. I like it.
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u/Pootis_1 17d ago
iirc the orbital inclination is also liked for earth observation stuff
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u/snoo-boop 17d ago
Sure, it's the 2nd most popular rideshare orbit after SSO.
Which has little to do with a crewed space station.
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u/Pootis_1 17d ago
Earth observation has never been the sole reason for a station being launched but almost every space station has done significant earth observation stuff
Skylab was in a 50 degree inclination orbit specifically to do earth observation
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u/snoo-boop 17d ago
Earth observation by uncrewed satellites has made many advances since Skylab.
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u/Pootis_1 17d ago
The point is stations do earth observation work still
Like NASA says as much it's not that hard to find this stuff out
There are multiple earth observation instruments on the ISS
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u/Triabolical_ 17d ago
This makes more sense than their last plan.
NASA has made little progress for commercial LEO and it appears there is no great business model.
With this model, NASA can save a lot of hardware and experiments and move them straight across, and it makes axiom the de facto next station.
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u/Mindless_Use7567 17d ago
What are you talking about the Axiom contract predates Commercial LEO Destinations by several years. Axiom was originally contracted to add 2 private modules to the ISS then Axiom chose to use is as a base to build a space station that would split off from the ISS and now due to financial and timing constraints they have had to rework the entire station concept.
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u/Triabolical_ 17d ago
NASA considers axiom to be one of the CLD partners
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u/Mindless_Use7567 17d ago
Yes because Axiom is allowed to apply for phase 2 contracts while Axiom Station was specifically forbidden from applying for phase 1 funding due to the earlier contract with NASA predating CLD.
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u/snoo-boop 17d ago
Axiom was always going to make it possible to move things straight across, before the Axiom segment detached from the ISS.
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u/Triabolical_ 17d ago
Yes. I mention it because commercial LEO is currently messed up as a program and a quicker axiom solution gives them better chances
The problem was that their old model took a long time and a lot of money to get to a free flyer.
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u/Decronym Acronyms Explained 17d ago edited 10d ago
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:
| Fewer Letters | More Letters |
|---|---|
| CLD | Commercial Low-orbit Destination(s) |
| Isp | Specific impulse (as explained by Scott Manley on YouTube) |
| Internet Service Provider | |
| KSC | Kennedy Space Center, Florida |
| LEO | Low Earth Orbit (180-2000km) |
| Law Enforcement Officer (most often mentioned during transport operations) | |
| SSO | Sun-Synchronous Orbit |
Decronym is now also available on Lemmy! Requests for support and new installations should be directed to the Contact address below.
5 acronyms in this thread; the most compressed thread commented on today has acronyms.
[Thread #704 for this sub, first seen 24th Dec 2024, 21:47]
[FAQ] [Full list] [Contact] [Source code]
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u/xerberos 17d ago
Axiom Station program manager and Chief Operating Officer Mark Greeley said in a company statement on Dec. 18. "With the International Space Station needing to protect for the ability to accommodate a deorbit vehicle on station, we were able to accelerate this work to support the program's requirements."
What the bleep does that mean?
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u/snoo-boop 16d ago
The deorbit plan requires leaving the deorbit vehicle docked in a particular place for a year before it's used.
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u/Glittering_Noise417 16d ago edited 10d ago
They better move fast. Multiple starships could accomplish the same thing for "far less" money and time, if NASA asked. Space X just need a centralized docking hub module to link multiple starships. Overtime they could disassemble the fuel tanks and recover even more space. 4 ships could easily have 20x the internal volume of ISS.
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u/mfb- 17d ago
So the new plan is just to dock the Payload, Power and Thermal module, then undock it to become an independent space station. No habitat module, not sure about life support, so visits might be limited by the life support system of the visiting capsule.
It also means no ISS support for any assembly steps. Having the first module on the ISS is still nice for testing, but it means the station has to go to the same inclination.