Author Topic: Station Boost With Dragon  (Read 6281 times)

Offline Jimmy10

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Station Boost With Dragon
« on: 08/07/2021 07:08 pm »
Given difficulties with Starliner (and for redundancy) is there anything that could be done with cargo Dragon in the unpressurised section to rig up an engine to boost the station?

Offline MattMason

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Re: Station Boost With Dragon
« Reply #1 on: 08/07/2021 07:31 pm »
This is not yet any configuration officially proposed by anyone as I know of. Nor may it be required.

As you probably know, the central ISS station boost vehicles have been: Shuttle Orbiters (retired), Progress resupply spacecraft (primary and preferred), ESA Autonomous Transfer Vehicle (retired), Northrup Grumman Cygnus, and Zvesda's two main engines.

The Cygnus is the only active US spacecraft used since the Orbiter's retirement for a station boost. I believe a boost was last done with OA-9 in 2018, and it worked fine. The Cygnus' advantage, like the Progress, is that it has a central engine, whereas Dragons have only maneuvering thrusters.

Adding a propulsive element on a Cargo Dragon might steal upmass from other supplies or hardware required. Adding such an engine to a Crew Dragon would likely be nixed since that adds to human flight risks, particularly in an abort.

Starliner's abort engines, like Crew Dragon's SuperDracos, are for aborts only. Not sure if there's any configuration to allow a throttled use of either for non-abort use.

It's possible that JAXA's upgraded HTV-X resupply vehicle could also do boosts once it's online.

I'm not in the industry at all; just noting some educated guesses.
« Last Edit: 08/07/2021 07:33 pm by MattMason »
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Offline Jimmy10

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Re: Station Boost With Dragon
« Reply #2 on: 08/07/2021 07:43 pm »
Thanks. Starliner can boost though?  Wonder if it has been looked at for cargo Dragons?

Offline rpapo

Re: Station Boost With Dragon
« Reply #3 on: 08/07/2021 11:32 pm »
Starliner's abort engines, like Crew Dragon's SuperDracos, are for aborts only. Not sure if there's any configuration to allow a throttled use of either for non-abort use.
No certified configuration.  Though in all seriousness, even though the SuperDracos can be throttled relatively well (they were designed for powered landing, after all), the minimum power level is still probably far above what anybody would want to use in pushing the ISS around.  That is a task that requires gentle pushes, not heavy slams.
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Offline rakaydos

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Re: Station Boost With Dragon
« Reply #4 on: 08/08/2021 12:00 am »
Starliner's abort engines, like Crew Dragon's SuperDracos, are for aborts only. Not sure if there's any configuration to allow a throttled use of either for non-abort use.
No certified configuration.  Though in all seriousness, even though the SuperDracos can be throttled relatively well (they were designed for powered landing, after all), the minimum power level is still probably far above what anybody would want to use in pushing the ISS around.  That is a task that requires gentle pushes, not heavy slams.
Superdraco's advantage is that there's 8 of them, and you only need 2 for balanced thrust. So that's 25% thrust before any throttling at all.

Online gongora

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Re: Station Boost With Dragon
« Reply #5 on: 08/08/2021 12:47 am »
The Crew Dragon Super Dracos are not going to be used for anything but aborts (any change would require removing some of the changes made after the DM-1 capsule exploded and requalifying the entire propulsion system), and Cargo Dragon doesn't have them.

Offline Comga

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Re: Station Boost With Dragon
« Reply #6 on: 08/08/2021 04:12 am »
It has to be kept clear that the concept is for Cargo Dragon to boost the ISS, presumably in the absence of the Russians.
Cargo Dragon has no Super Dracos.
We can take gongora’s post as certain, that Crew Dragon is not going to be used for Station orbit maintenance or debris avoidance maneuvers.
We can agree with rpapo that there is no certified configuration for this.
We can agree with MattMason that it “may not be needed” but organizations prepare for all sorts of contingencies that are only possibilities.
So the point would be to think of the more probable configurations and see if NASA ever makes public anything like them.

One might be to install extra (2-8) regular Dracos in the now empty Super Dracos cowlings on Cargo Dragons. Simpler plumbing and wiring than putting thrusters in the trunk. Not much extra mass besides the dedicated fuel. Then if there was a way to dock or berth it to the “back”, now the Russian end, facing forward, it could act like the now retired ATVs. Put back some or all of the Crew Dragon fuel tanks and there would be plenty of boost capacity.

Does anyone here have the values for the axial thrust of Zvezda, Progress, ATV, or the Dracos and Super Dracos (including cosine losses)?
How about Isp and fuel capacity for Progress and Crew Dragon tanks?
Would an IDA compliant docking adapter added to the back support this use?
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline jrhan48

Re: Station Boost With Dragon
« Reply #7 on: 08/08/2021 12:29 pm »
It has to be kept clear that the concept is for Cargo Dragon to boost the ISS, presumably in the absence of the Russians.
Cargo Dragon has no Super Dracos.
We can take gongora’s post as certain, that Crew Dragon is not going to be used for Station orbit maintenance or debris avoidance maneuvers.
We can agree with rpapo that there is no certified configuration for this.
We can agree with MattMason that it “may not be needed” but organizations prepare for all sorts of contingencies that are only possibilities.
So the point would be to think of the more probable configurations and see if NASA ever makes public anything like them.

IMHO if I remember correctly, the upcoming Dream Chaser cargo vessel from Sierra Nevada has or will have a reboost capability, may require additional hardware resources they are developing, se the "Shooting Star Transport Vehicle"

Offline Jim

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Re: Station Boost With Dragon
« Reply #8 on: 08/09/2021 06:25 pm »
Wonder if it has been looked at for cargo Dragons?

Their thruster locations are not the best

Offline nacnud

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Re: Station Boost With Dragon
« Reply #9 on: 08/09/2021 06:54 pm »
So boost with Dragon without modifications seems foolish when Cygnus could do the job. And modifying Dragon seems foolish when development at SpaceX is so focused on Starship.

Could the new Axiom modules boost the station, for as long as they are attached anyway.

Offline Zed_Noir

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Re: Station Boost With Dragon
« Reply #10 on: 08/10/2021 06:28 am »
A Dragon XL could boost the ISS with its RCS thrusters along with adding more pressurized volume to the ISS. Presuming there will be a Dragon XL, that it isn't replaced with some variant of the Lunar Starship for Gateway logistics.

Online darkenfast

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Re: Station Boost With Dragon
« Reply #11 on: 08/10/2021 10:08 am »
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Offline TrevorMonty

Re: Station Boost With Dragon
« Reply #12 on: 08/10/2021 06:22 pm »
Cygnus is getting updated for station boosting.

https://forum.nasaspaceflight.com/index.php?topic=21179.msg2274831#msg2274831
I assume NGIS did this upgrade at NASA's request. Unless there is financial incentive or relibility issue why modify such reliable vehicle.



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Offline Zed_Noir

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Re: Station Boost With Dragon
« Reply #13 on: 08/11/2021 04:14 am »
Cygnus is getting updated for station boosting.

https://forum.nasaspaceflight.com/index.php?topic=21179.msg2274831#msg2274831
I assume NGIS did this upgrade at NASA's request. Unless there is financial incentive or relibility issue why modify such reliable vehicle.



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Maybe to test out systems for the HALO module for the Lunar Gateway mention in the tweet by Marcia Smith.

Offline RoadWithoutEnd

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Re: Station Boost With Dragon
« Reply #14 on: 08/11/2021 06:13 am »
Knowing the history and (mostly diplomatic) purpose of ISS, I wouldn't trust decision-making about boost servicing to be logical or cost-conscious.  So the merits of Dragon for the purpose would be almost irrelevant to what they end up doing.

By now boost servicing shouldn't even be necessary.  The station should have been outfitted with electric thrusters and requisite power sources ages ago.  But every contract toward that has been canceled with hand-wavy excuses, almost certainly to preserve the economic value of the need for regular boost servicing.

Meanwhile the Chinese station has electric propulsion systems flying and operational.

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Offline Jim

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Re: Station Boost With Dragon
« Reply #15 on: 08/11/2021 01:04 pm »

By now boost servicing shouldn't even be necessary.  The station should have been outfitted with electric thrusters and requisite power sources ages ago.


Wrong for many reasons.
A.  The existing thrusters would still be needed for CMG desat
B.  Electric thrusters still need propellant servicing
C.  Electric thrusters would ruin the micro gravity environment negating the major reason the ISS exists
D.  power sources were not available ages ago
E.  Electric thrusters can't make collision avoidance maneuvers

Meanwhile the Chinese station has electric propulsion systems flying and operational.

a meaningless point.  The above points still apply.
« Last Edit: 08/11/2021 01:08 pm by Jim »

Offline Jim

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Re: Station Boost With Dragon
« Reply #16 on: 08/11/2021 01:06 pm »

Maybe to test out systems for the HALO module for the Lunar Gateway mention in the tweet by Marcia Smith.

The HALO module has no propulsion or attitude control.  That is what PPE is for.

Offline baldusi

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Re: Station Boost With Dragon
« Reply #17 on: 08/11/2021 05:35 pm »
Dragon 2 has most of it's thrusters on the fore, around the docking port. And the SuperDragons have too much thrust and no lateral. So Dragon 2 is the wrong platform for reboosts. There's a reason the US has multiple visiting vehicles and so you shouldn't try to make Dragon do it all.

Offline Asteroza

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Re: Station Boost With Dragon
« Reply #18 on: 08/11/2021 11:48 pm »
C.  Electric thrusters would ruin the micro gravity environment negating the major reason the ISS exists

I've always been bothered by that stance, since atmospheric drag by definition is messing with the microgravity environment onboard ISS.

Is the claim that continuous variable small thrust by electric propulsion counteracting drag in realtime isn't feasible leading to the thinking that you would then have to have continuous electric thrust at the average drag rate, thus leading to random undesired movement due to imbalance between constant thrust and instantaneous air drag ruining the microgravity environment? I'm having trouble reconciling that with how that would that be qualitatively worse than random air drag also messing with the microgravity environment?

Offline Jorge

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Re: Station Boost With Dragon
« Reply #19 on: 08/12/2021 01:55 am »
C.  Electric thrusters would ruin the micro gravity environment negating the major reason the ISS exists

I've always been bothered by that stance, since atmospheric drag by definition is messing with the microgravity environment onboard ISS.

Is the claim that continuous variable small thrust by electric propulsion counteracting drag in realtime isn't feasible leading to the thinking that you would then have to have continuous electric thrust at the average drag rate, thus leading to random undesired movement due to imbalance between constant thrust and instantaneous air drag ruining the microgravity environment? I'm having trouble reconciling that with how that would that be qualitatively worse than random air drag also messing with the microgravity environment?

The original phrasing of Ockham's razor was, "entities should not be multiplied beyond necessity".

Jim is still right, but he could have made his point with A and E; the others are superfluous and it's pointless to argue them as long as A and E exist.
JRF

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