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Hubble servicing after 2010
by
brihath
on 04 Aug, 2007 19:25
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In reading about the next HST Servicing Mission, one of the tasks will be to add a docking collar to the base of the HST to support either future servicing missions or a deorbit stage. I have some thoughts regarding servicing HST after 2010 that I would like to lay on the table and solicit some opinions about.
What would be the possibility of attaching a maneuver stage to the base of HST and using it to change its orbit from the current 28.5 degree inclination to the ISS 51 degree inclination? My thinking is that, if the orbits of both spacecraft were on the same inclination, the HST could be maneuvered to the vicinity of the ISS, which could be used as a base for future HST repairs.
Now, I understand that changing the orbital inclination by that amount requires a large dV, but I also remember that back in 1997, I believe, Hughes used a lunar swingby maneuver to change the orbit of AsiaSat 3 from a 51 degree inclination to equatorial, a much larger inclination change. This maneuver was done using only onbard spaccraft propellant, and enough propellant was left on board for it to have a useful, though shortened on orbit lifetime.
My thinking is that with the very limited EVA capability of Orion, future servicing missions are not likely, so the only use of the docking collar would be for a deorbit stage, which is a real shame, given the science contributions of Hubble to date. However, the ISS has proven to be a very viable EVA platform, and will be for years to come.
Replacement components could be lofted using the ATV, HTV, or COTS if and when they fly. since the infrastructure would be in place for logistics (I hope, but that is a different topic), the required components could be flown for less incremental cost than a current Shuttle servicing mission. Since the crew is already in place, those resources already exist, and the HST has a grapple device that could be used either to hold it in place or to dock it to a servicing fixture.
Now there are some who will say that Hubble will be redundant after JWST is operational, but I don't treat them as mutually exclusive. To use an earthbound analogy, Palomar is still functioning and contributing science even though far more capable telescopes are operational.
How long Hubble's life could be extended is an open question, but having replacement CMG's or batteries could sustain on orbit capability and science output, even if the science instruments are not improved and replaced.
I am assuming that science would not suffer from the inclination change.
I guess my question is twofold:
Technical- Is it doable? What resources would be required to make it happen?
Financial- Would it be more costly than a Shuttle servicing mission? Given the fact that subsequent servicing mssions could be mounted following relocation of HST, would it make financial sense?
BTW- I floated this idea in a letter to the editor that was published in AW&ST magazine a couple of years ago before the currently planned HST servicing mission was approved.
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#1
by
Chris Bergin
on 04 Aug, 2007 19:35
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Officially NASA say this is the last servicing mission, and LIDS is to be installed for the purpose of making that life-ending deorbit easier to carry out.
http://www.nasaspaceflight.com/content/?cid=4881 (Note the headline was because it was before the official announcement):
Sources also note that Discovery will carry a passive LIDS (Low Impact Docking System) to be attached to Hubble's aft bulkhead. The requirement is to provide a capability to enable a future spacecraft to perform an autonomous rendezvous and docking with Hubble. This can be used for a future deorbit mission, or even another servicing mission via Orion.
So there will be capability, but whether the will is there for NASA to service via Orion....that's the $64m question (plus a few more million
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I'll leave the other questions to those who are better briefed on HST.
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#2
by
MKremer
on 04 Aug, 2007 20:24
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It'd probably take the equivalent of an ET (or two) worth of fuel for that much delta-v and inclination change. Plus, Hubble needs the higher orbit (twice as high as it is now would be even better) to minimize orbital decay while still being accessable for servicing - Hubble has no -zero- attitude or maneuvering thrusters.* It needs to be a rock-stable imaging platform for long periods, so no random liquid flows or banging solenoids and valves.
*Which is why putting it anywhere near the ISS isn't a very good idea.
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#3
by
brihath
on 04 Aug, 2007 20:35
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MKremer - 4/8/2007 4:24 PM
It'd probably take the equivalent of an ET (or two) worth of fuel for that much delta-v and inclination change. Plus, Hubble needs the higher orbit (twice as high as it is now would be even better) to minimize orbital decay while still being accessable for servicing - Hubble has no -zero- attitude or maneuvering thrusters.* It needs to be a rock-stable imaging platform for long periods, so no random liquid flows or banging solenoids and valves.
*Which is why putting it anywhere near the ISS isn't a very good idea.
I understand, but I am not saying that Hubble would stay berthed at ISS, only in a co-planar orbit with servicing rendezvous as necessary. Currently. Hubble doesn't have maneuvering thrusters, but KH-11's do, and they are approximately the same size as Hubble. They just focus their optics downward instead of into space.
Also, rememember that the AsiaSat 3 inclination change was done using only onboard maneuvering fuel and thrusters (100 lb thruster, I think). I realize that AsiaSat 3 was already in a geosynchronous transfer orbit, and the final orbit was geosynchronous. I guess what I am wondering how much fuel would be required for the Hubble to do a lunar swingby inclination change. Another consideration is that there may be much more available time to do it. I believe lunar transit time for AsiaSat was on the order of five days, about double the Apollo timeline.
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#4
by
Danny Dot
on 04 Aug, 2007 20:38
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Chris Bergin - 4/8/2007 2:35 PM
Officially NASA say this is the last servicing mission, and LIDS is to be installed for the purpose of making that life-ending deorbit easier to carry out.
snip
Does anybody but NASA deoribit its satellites after they need to be replaced. How about the imaging services and the LOE sat-phone guys. On the same subject, after their upperstage inserts them what happens to the upperstage. A college professor told my class upperstages are typically left in LEO and orbital decay brings them down. Is this industry standard?
Danny Deger
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#5
by
MKremer
on 04 Aug, 2007 20:40
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KH-11s aren't required to maintain pointing precision at .01 arcsecond for up to 24 hours at a time. (That's the equivalent of not varying more than the width of a dime placed 350 miles away.)
Also, without being able to maneuver how would it be able to avoid the higher chance of MMOD collisions at that lower altitude?
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#6
by
brihath
on 04 Aug, 2007 20:47
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MKremer - 4/8/2007 4:40 PM
They also aren't required to maintain pointing precision at .01 arcsecond for up to 24 hours at a time. (That's the equivalent of not varying more than the width of a dime placed 350 miles away.)
I imagine pointing precision requirements for KH-11's are classified, so I can't say what their requirements are. I'm not sure it is germane to the argument. I'm not saying thrusters would be used for attitude control-only for the inclination change or to rendezvous with ISS. Otherwise they would hand over fine pointing control to the current internal Hubble system. Science operations would be on hiatus during these events, just as they are during Servicing Missions.
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#7
by
MKremer
on 04 Aug, 2007 20:58
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Any liquid mass at all would add unacceptable pointing fluctuations because it would constantly be in random motion (conservation of momentum and inertia) - you couldn't dampen *all* the movement of any propellent, at least not within any reasonable time frame after each pointing change.
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#8
by
psloss
on 04 Aug, 2007 21:04
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brihath - 4/8/2007 4:35 PM
I understand, but I am not saying that Hubble would stay berthed at ISS, only in a co-planar orbit with servicing rendezvous as necessary. Currently. Hubble doesn't have maneuvering thrusters, but KH-11's do, and they are approximately the same size as Hubble. They just focus their optics downward instead of into space.
I think variations of this question have been asked here before (
example of one thread), but it's an interesting exercise.
One of the questions: let's say you've already completed the plane change and it's time for servicing...what is going to maneuver HST back and forth between its science/ops altitude (~600 km) and the ISS altitude (300-400 km)?
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#9
by
Andy_Small
on 04 Aug, 2007 21:19
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why couldn't a telescope like HST or HST itself for that matter be attached to ISS so it could be serviceable anytime via EVA?
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#10
by
brihath
on 04 Aug, 2007 21:19
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MKremer - 4/8/2007 4:58 PM
Any liquid mass at all would add unacceptable pointing fluctuations because it would constantly be in random motion (conservation of momentum and inertia) - you couldn't dampen *all* the movement of any propellent, at least not within any reasonable time frame after each pointing change.
OK- if that is a constraint to pointing accuracy, then the mission model would be to do the inclination change, bring it to the vicinity of ISS for servicing, then return it to a suitable operational coplanar orbit. At that point in time, the maneuvering module could be jettisoned.
As a cost issue, another maneuvering module would be required for subsequent servicing missions, albeit with less fuel as the inclination change would not be required. I can't forsee servicing missions occurring in less than five year intervals, unless something fails.
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#11
by
Jim
on 04 Aug, 2007 21:20
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Danny Dot - 4/8/2007 4:38 PM
Chris Bergin - 4/8/2007 2:35 PM
Officially NASA say this is the last servicing mission, and LIDS is to be installed for the purpose of making that life-ending deorbit easier to carry out.
snip
Does anybody but NASA deoribit its satellites after they need to be replaced. How about the imaging services and the LOE sat-phone guys. On the same subject, after their upperstage inserts them what happens to the upperstage. A college professor told my class upperstages are typically left in LEO and orbital decay brings them down. Is this industry standard?
Danny Deger
US launches including NASA have to account for orbital debris, either disposal orbits, naturally decaying orbits or deorbit burns
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#12
by
brihath
on 04 Aug, 2007 21:21
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Andy_Small - 4/8/2007 5:19 PM
why couldn't a telescope like HST or HST itself for that matter be attached to ISS so it could be serviceable anytime via EVA?
That goes back to the pointing accuracy issue. ISS has way too many random motions.
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#13
by
Andy_Small
on 04 Aug, 2007 21:22
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brihath - 4/8/2007 4:21 PM
Andy_Small - 4/8/2007 5:19 PM
why couldn't a telescope like HST or HST itself for that matter be attached to ISS so it could be serviceable anytime via EVA?
That goes back to the pointing accuracy issue. ISS has way too many random motions.
ah that makes sence. To bad that would be a real nice platform otherwise
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#14
by
Jim
on 04 Aug, 2007 21:24
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Not viable
1. HST thermal systems are not designed for 51 degrees
2. the servicing hardware still has to be delivered to the ISS, so just go to the HST instead
3. The ISS is a dirty environment, outgassings, thrusters, H02, H2 venting etc
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#15
by
psloss
on 04 Aug, 2007 21:36
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Jim - 4/8/2007 5:24 PM
2. the servicing hardware still has to be delivered to the ISS, so just go to the HST instead
In the hypothetical of ISS servicing then wouldn't that mean two launches for each servicing mission? One to deliver the SM hardware to ISS and the other with the tug for HST?
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#16
by
Jim
on 04 Aug, 2007 22:03
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psloss - 4/8/2007 5:36 PM
Jim - 4/8/2007 5:24 PM
2. the servicing hardware still has to be delivered to the ISS, so just go to the HST instead
In the hypothetical of ISS servicing then wouldn't that mean two launches for each servicing mission? One to deliver the SM hardware to ISS and the other with the tug for HST?
That's what I mean, just go to HST
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#17
by
brihath
on 04 Aug, 2007 22:05
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Jim - 4/8/2007 5:24 PM
Not viable
1. HST thermal systems are not designed for 51 degrees
2. the servicing hardware still has to be delivered to the ISS, so just go to the HST instead
3. The ISS is a dirty environment, outgassings, thrusters, H02, H2 venting etc
1. Can you be more specific regarding what thermal systems are required for 51 vs 28 degrees? How is the thermal environment different at higher orbital inclinations? Also, wasn't ISS going to go to 28 degrees when it was SSF? Were there substantial changes in thermal design when the change was made?
2. OK, but we currently don't have the capability to do that post shuttle. I don't think it is realistic to expect servicing EVA's from Orion- no air lock, limited room for tools fixtures, etc.
3. No science would be performed in the vcinity of ISS, so the sunshade would be closed. During servicing at Shuttle, other systems still operate on shuttle, so I suspect there is still some outgassing occurring.
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#18
by
brihath
on 04 Aug, 2007 22:10
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psloss - 4/8/2007 5:36 PM
Jim - 4/8/2007 5:24 PM
2. the servicing hardware still has to be delivered to the ISS, so just go to the HST instead
In the hypothetical of ISS servicing then wouldn't that mean two launches for each servicing mission? One to deliver the SM hardware to ISS and the other with the tug for HST?
That's correct- there would be more than one launch required, but any required components could be delivered by existing logistics vehicles, and they could be delivered over time so they are on station when needed. Since they would be included with other cargo, they total cost burden of the launch would be shared with other cargo. That is why I stipulated using existing infrastructure at the time.
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#19
by
psloss
on 04 Aug, 2007 22:21
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brihath - 4/8/2007 6:10 PM
That's correct- there would be more than one launch required, but any required components could be delivered by existing logistics vehicles, and they could be delivered over time so they are on station when needed. Since they would be included with other cargo, they total cost burden of the launch would be shared with other cargo. That is why I stipulated using existing infrastructure at the time.
The point is how much this is going to cost...for example, is the HST hardware sized such that it can be mixed efficiently with ISS logistics? (Since it is currently sized to fit in the orbiter payload bay.)
Have you worked out a SWAG for the costs for the plane change mission plus a couple of servicing missions? Ultimately, the question is how much money is worth spending to extend HST ops past whatever SM-4 gives it.
)