Author Topic: Building a Spacecraft to Deorbit ISS 'Not Optional'.  (Read 5475 times)

Offline Stan-1967

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Re: Building a Spacecraft to Deorbit ISS 'Not Optional'.
« Reply #20 on: 10/28/2023 05:31 pm »
It is going to need about 15 tons of biprop.

So the existing Cygnus PCM looks to have enough internal volume for 15 tons of prop.  Would a modified Cygnus focus on converting the internal volume to tankage that feeds the service module?  Alternately do you shrink the Cygnus PCM, keeping just the docking interface, and integrate larger tanks into the service module? 

ISTM that pressure fed hypergolics probably would favor not doing a "crossfeed" from tanks in the PCM, and rather would prefer expanding the tanks of the SM.  It may also be that the SM control system is not designed for controlling a near 18t fully loaded vehicle.  No easy modifications look possible.

Also looks like Vulcan, FH, and maybe F9 ( expendable) could get it to the ISS within a standard fairing.
« Last Edit: 10/28/2023 05:37 pm by Stan-1967 »

Offline bobthemonkey

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Re: Building a Spacecraft to Deorbit ISS 'Not Optional'.
« Reply #21 on: 10/28/2023 07:51 pm »
The Cygnus SM is derived from reasonably standardised components from various LEO and Satellite buses, and there was some design work (unsure whether it went further than conceptual) for an unpressurised cargo carrier variant of Cygnus. This was essentially a strongback/spine for unpressurised payloads with a CBM up front.

It wouldn't be too far of a stretch (keeping in mind Jims 'Rockets aren't Lego' maxim) to see a similar design reappear, but with multiple existing bi-prop tanks instead of ORUs linked to some kind of manifold feeding into the existing SM fuel system - possibly with additional engines for redundancy.

Online Yellowstone10

Are you proposing equipping Cygnus with an alternate engine?

What existing engines are there in that 3 to 6 kN thrust range, I wonder? (With the exception of the KTDU-80 on the Soyuz, because I suspect that's politically infeasible.)

Online Yellowstone10

I believe you, but I am too ignorant to know why this is true, so I would appreciate it if you would educate me. If the earlier small burns get it low enough, maybe that last Cygnus would not have enough energy to cause a precise enough de-orbit?

I think that's exactly the case. You need one spacecraft with enough delta-V to drop the ISS from "low-but-stable orbit" to "will do exactly one-half more orbit before it's in the drink" in one burn. If you stop halfway through, then who knows how many more perigees it can survive before re-entry? And each of those perigees is 2,200 km west of the previous one.

Offline Zed_Noir

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Re: Building a Spacecraft to Deorbit ISS 'Not Optional'.
« Reply #24 on: 10/28/2023 11:14 pm »
<snip>
To this point, the deorbit vehicle requires at least 3.2kN (up to 6.2 kN desired) of thrust for the final deorbit burn / entry shaping.
Cygnus is currently equipped with one BT-4 (developing 0.5kN of thrust) which is significantly below the thrust requirements.

Quote from: ISS Deorbit USOS Concept of Operations Overview - Design Considerations
The deorbit vehicle will need to provide at least 3236 N thrust to hit the target delta v (30 m/s) within a 60 minute time period.

Is the proposal to create a 7 - 13 engined Cygnus?
Are you proposing equipping Cygnus with an alternate engine?
Estimate modifying the Cygnus with additional engines and extra tankage versus building a new spacecraft is about the same cost.

Online DanClemmensen

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Re: Building a Spacecraft to Deorbit ISS 'Not Optional'.
« Reply #25 on: 10/30/2023 09:02 pm »

One thing to remember is that according to current plans, the forward CBM of the Harmony module will be empty with the PMA-2/IDA-2 having been relocated when the first Axiom module arrives.
Yuck. I was thinking(?) fantasizing that the only spacecraft currently being developed that can Deorbit ISS, without any hardware modifications, is Starship HLS. But if it cannot dock its nose IDSS port to Harmony forward, then hardware development would be needed to dock it to some appropriate place on ISS, and a custom solution might be cheaper after all.

If PMA-2+IDA-2 were still in place, an instance of Starship HLS would probably work nicely, and the deorbit mission could probably be designed so HLS could undock and save itself instead of going down with ISS. It would then be available in the correct plane to become a module of the Axiom station.
« Last Edit: 10/30/2023 09:03 pm by DanClemmensen »

Offline Zed_Noir

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Re: Building a Spacecraft to Deorbit ISS 'Not Optional'.
« Reply #26 on: 10/30/2023 10:19 pm »

One thing to remember is that according to current plans, the forward CBM of the Harmony module will be empty with the PMA-2/IDA-2 having been relocated when the first Axiom module arrives.
Yuck. I was thinking(?) fantasizing that the only spacecraft currently being developed that can Deorbit ISS, without any hardware modifications, is Starship HLS. But if it cannot dock its nose IDSS port to Harmony forward, then hardware development would be needed to dock it to some appropriate place on ISS, and a custom solution might be cheaper after all.
<snip>
Could bring up a self propelled adapter module that got the IDSS docking ring on end and the Russian SSVP docking system on the other end in the HLS cargo hold. Then push with the HLS with the adapter module from the Russian side of the ISS. Of course getting a SSVP docking system might be problematic. Maybe Roscosmos is open to some sort of bartering.

Offline Jim

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Re: Building a Spacecraft to Deorbit ISS 'Not Optional'.
« Reply #27 on: 10/31/2023 12:49 am »

Yuck. I was thinking(?) fantasizing that the only spacecraft currently being developed that can Deorbit ISS, without any hardware modifications, is Starship HLS. But if it cannot dock its nose IDSS port to Harmony forward, then hardware development would be needed to dock it to some appropriate place on ISS, and a custom solution might be cheaper after all.

If PMA-2+IDA-2 were still in place, an instance of Starship HLS would probably work nicely, and the deorbit mission could probably be designed so HLS could undock and save itself instead of going down with ISS. It would then be available in the correct plane to become a module of the Axiom station.

that would be wrong.  too high of thrust. And it can not undock.   Entry is too close to deorbit.

Online DanClemmensen

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Re: Building a Spacecraft to Deorbit ISS 'Not Optional'.
« Reply #28 on: 10/31/2023 01:23 am »

Yuck. I was thinking(?) fantasizing that the only spacecraft currently being developed that can Deorbit ISS, without any hardware modifications, is Starship HLS. But if it cannot dock its nose IDSS port to Harmony forward, then hardware development would be needed to dock it to some appropriate place on ISS, and a custom solution might be cheaper after all.

If PMA-2+IDA-2 were still in place, an instance of Starship HLS would probably work nicely, and the deorbit mission could probably be designed so HLS could undock and save itself instead of going down with ISS. It would then be available in the correct plane to become a module of the Axiom station.
that would be wrong.  too high of thrust. And it can not undock.   Entry is too close to deorbit.
I was assuming an HLS with mid-mounted hot gas lunar landing thrusters. If it cannot save itself, then it's expended, and you would of course use a minimal configuration, not a fully-configured HLS. However, even though Starships are relatively cheap, the cost is high enough that it may exceed the cost designing and manufacturing a special-purpose deorbiter. It's a non-starter anyway if the Harmony forward IDSS dock is absent.

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