Author Topic: L1/2 spacestation with depot  (Read 64676 times)

Offline Archibald

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Re: L1/2 spacestation with depot
« Reply #100 on: 02/01/2010 06:27 am »
I suggest the name Emily for the EML- facility.
If we ever build one at Sun-Earth L1 it might be called Sally;
while a Sun-Mars L1 station might be Samuel :)

There had been a lot of talk about telescope servicing missions recently.

According to this article discussing Belbruno trajectories
http://www.thespacereview.com/article/569/1

Quote
The most fascinating, though, is a way that—theoretically—could allow future servicing of the James Webb Space Telescope (JWST). Unlike Hubble, which is in low Earth orbit, JWST will be located at the Earth-Sun L2 Lagrange point, about 1.5 million kilometers from the Earth. Whereas Hubble was designed to be regularly repaired and upgraded by shuttle missions, there are no plans to make JWST servicable because of its location. However, Folta said there is a way around this by taking advantage of the intersections between Sun-Earth and Earth-Moon dynamics that would allow JWST to maneuver back closer to the Earth. “Because of this intersection we could actually bring the JWST back into the Earth-Moon system. Someone could go out into the Earth-Moon system in three or four days and repair what they needed do, and then we could send JWST back out.” The cost of doing that, in terms of propellant for JWST? Two kilograms, according to Folta.
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Offline Robotbeat

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Re: L1/2 spacestation with depot
« Reply #101 on: 02/01/2010 11:49 pm »
...
According to this article discussing Belbruno trajectories
http://www.thespacereview.com/article/569/1

Quote
The most fascinating, though, is a way that—theoretically—could allow future servicing of the James Webb Space Telescope (JWST). Unlike Hubble, which is in low Earth orbit, JWST will be located at the Earth-Sun L2 Lagrange point, about 1.5 million kilometers from the Earth. Whereas Hubble was designed to be regularly repaired and upgraded by shuttle missions, there are no plans to make JWST servicable because of its location. However, Folta said there is a way around this by taking advantage of the intersections between Sun-Earth and Earth-Moon dynamics that would allow JWST to maneuver back closer to the Earth. “Because of this intersection we could actually bring the JWST back into the Earth-Moon system. Someone could go out into the Earth-Moon system in three or four days and repair what they needed do, and then we could send JWST back out.” The cost of doing that, in terms of propellant for JWST? Two kilograms, according to Folta.
That's exactly what I was thinking about, a while back. Why go to ESL2 when you can just go to EML1/2?
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Offline Hop_David

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Re: L1/2 spacestation with depot
« Reply #102 on: 02/02/2010 12:26 am »
...
According to this article discussing Belbruno trajectories
http://www.thespacereview.com/article/569/1

Quote
The most fascinating, though, is a way that—theoretically—could allow future servicing of the James Webb Space Telescope (JWST). Unlike Hubble, which is in low Earth orbit, JWST will be located at the Earth-Sun L2 Lagrange point, about 1.5 million kilometers from the Earth. Whereas Hubble was designed to be regularly repaired and upgraded by shuttle missions, there are no plans to make JWST servicable because of its location. However, Folta said there is a way around this by taking advantage of the intersections between Sun-Earth and Earth-Moon dynamics that would allow JWST to maneuver back closer to the Earth. “Because of this intersection we could actually bring the JWST back into the Earth-Moon system. Someone could go out into the Earth-Moon system in three or four days and repair what they needed do, and then we could send JWST back out.” The cost of doing that, in terms of propellant for JWST? Two kilograms, according to Folta.
That's exactly what I was thinking about, a while back. Why go to ESL2 when you can just go to EML1/2?

If faulty memory serves, at ESL2 you can shield the scope from 3 major light pollution sources (sun, earth, moon) with a single shade. Those 3 bodies are also sources of infra red light.

As the quoted paragraph mentions, the delta V between EML1/2 and ESL2 is small. But I would suspect it would be time consuming trip.

Offline daveklingler

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Re: L1/2 spacestation with depot
« Reply #103 on: 02/02/2010 07:06 am »
Without the internet and probably this forum, most people would never have gotten to know propellant depots or the L points really... Everybody would just assume heavy lifters and LOR or EOR-LOR.

As I pointed out in one of the other forums, the original Space Transportation System (the "STS" in shuttle mission names) called for shuttles, a propellant depot/station and a couple of NTR tugs.

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Offline Robotbeat

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Re: L1/2 spacestation with depot
« Reply #104 on: 02/02/2010 03:37 pm »
...
According to this article discussing Belbruno trajectories
http://www.thespacereview.com/article/569/1

Quote
The most fascinating, though, is a way that—theoretically—could allow future servicing of the James Webb Space Telescope (JWST). Unlike Hubble, which is in low Earth orbit, JWST will be located at the Earth-Sun L2 Lagrange point, about 1.5 million kilometers from the Earth. Whereas Hubble was designed to be regularly repaired and upgraded by shuttle missions, there are no plans to make JWST servicable because of its location. However, Folta said there is a way around this by taking advantage of the intersections between Sun-Earth and Earth-Moon dynamics that would allow JWST to maneuver back closer to the Earth. “Because of this intersection we could actually bring the JWST back into the Earth-Moon system. Someone could go out into the Earth-Moon system in three or four days and repair what they needed do, and then we could send JWST back out.” The cost of doing that, in terms of propellant for JWST? Two kilograms, according to Folta.
That's exactly what I was thinking about, a while back. Why go to ESL2 when you can just go to EML1/2?

If faulty memory serves, at ESL2 you can shield the scope from 3 major light pollution sources (sun, earth, moon) with a single shade. Those 3 bodies are also sources of infra red light.

As the quoted paragraph mentions, the delta V between EML1/2 and ESL2 is small. But I would suspect it would be time consuming trip.

What I was meaning is that any human service mission wouldn't need to go all the way to ESL2. The telescope at ESL2 can send itself to EML1/2 with less than a year's worth of station-keeping propellant. The telescope can take its time to go to EML1/2 if it really needs servicing.
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Offline Archibald

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Re: L1/2 spacestation with depot
« Reply #105 on: 02/02/2010 07:49 pm »
Quote
But I would suspect it would be time consuming trip.

One to three years

Btw, I just love this picture http://forum.nasaspaceflight.com/index.php?action=dlattach;topic=13532.0;attach=86198;image
« Last Edit: 02/02/2010 07:55 pm by Archibald »
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Offline butters

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Re: L1/2 spacestation with depot
« Reply #106 on: 02/02/2010 09:14 pm »
I have a number of problems with the L1 Gateway proposal.

1) It doesn't have a propellant depot.

2) It specifies an expendable two-stage lander.

These problems can be fixed by using a docked reusable single-stage lander as a propellant depot.  The lander is the only client for the depot anyway.  The propellant would likely be NTO/MMH or H2O2/RP-1.

3) ISS staging with propulsive braking isn't going to happen.

Maybe a layover at ISS on the way out if the upper stage is to be refilled in LEO for TLI, but return from EML will be direct reentry.

4) Monolithic station imposes unnecessary mass constraints.

The lithium-ion fiber cells to be woven into composite partitions and inflatable skin is a particularly pie in the sky mass optimization.  The station can be launched into three pieces (docking/service module, habitat module, EVA/robotics module), assembled in LEO along with the docked lander (dry), and slowly spiraled out to EML by the SEP.

So you need the station modules, the lander, the SEP tug, the crew transport vehicle, a big enough launch vehicle or cryogenic propellant tankers, storable propellant tankers, and MPLMs.  Piece of cake...
« Last Edit: 02/02/2010 09:18 pm by butters »

Offline A_M_Swallow

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Re: L1/2 spacestation with depot
« Reply #107 on: 02/02/2010 10:28 pm »
Quotes by butters
"So you need the station modules,"
Under development by Bigelow.

"the lander,"
New project.

"the SEP tug,"
A VASIMR SEP tug is probably under development by Ad Astra

"the crew transport vehicle,"
At LEO - Dragon and Dream Chaser.
Else where - New project.

"a big enough launch vehicle"
For people Falcon 9 and man-rated Atlas V under development.
For propellant Falcon 9, Taurus II, Falcon 1, Atlas V and Delta IV.

"or cryogenic propellant tankers,"
New project.

"storable propellant tankers,"
Something for the oil companies to invent.

"and MPLMs."
A Multi-Purpose Logistics Module may or may not exist.


" Piece of cake..."
I will go to the shops.   ;D


The spacestation is also likely to need spacecraft repair facilities like robotic arms.  The same arms may be able to perform cargo transfer between spacecraft.

Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #108 on: 02/02/2010 10:36 pm »
So you need the station modules, the lander, the SEP tug, the crew transport vehicle, a big enough launch vehicle or cryogenic propellant tankers, storable propellant tankers, and MPLMs.  Piece of cake...

You'd want an incremental path towards this.

You could start with the lander itself, which could serve as a mini space station, depot and lander. Then you could add a hab. You could also do this in the reverse order. The hab would likely be a Bigelow hab to avoid unnecessary R&D. Then you could add a SEP tug. If it is only used between L1/L2 and GEO or LLO or in support of exploration to Mars orbit it doesn't have to cross the van Allens repeatedly. This makes it easier to field a first version quickly since that can be done with current technologies. You could also use low energy trajectories and chemical propulsion until the tug was ready.
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Offline butters

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Re: L1/2 spacestation with depot
« Reply #109 on: 02/02/2010 11:42 pm »
To get crew to EML without EOR or LEO refill requires an LV bigger than EELV Heavy, approximately 50mT IMLEO.  Dragon and Dream Chaser don't have the habitable volume and life-support for a 6-day trip (each way) on their own.  So the CTV is an Orion-like 20mT through TLI.

The CTV could be as light as 16mT through TLI with an expendable hab module (e.g. Dragon + Sundancer), launched on two F9s.  That still puts the EDS slightly out of the range of Atlas V 551, and Dragon would be a bit short of the dV to push itself and Sundancer through ROI.

Dragon really needs at least twice as much propellant to play this role.  The tankage may not fit in the capsule, and it may be more appropriate to add another propulsion system in the expendable trunk.  This probably exceeds the performance capability of F9.  It may be able to go on Atlas V 402.

Forget about LEO staging to an exoatmospheric CTV.  The propulsive braking required to return to LEO involves a round-trip dV of at least 7.5 km/s to EML1.  That makes the EDS considerably bigger than it would be for a heavier direct reentry CTV.

So it's not so simple.  Orion (the original reusable spec) was actually close to the ideal CTV because it could get away with not having an expendable hab in this role.  It would be nice to have an LV that could do 25mT IMLEO without any strap-ons (CTV) and up to 40mT with solid strap-ons (EDS).
« Last Edit: 02/02/2010 11:43 pm by butters »

Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #110 on: 02/02/2010 11:46 pm »
To get crew to EML without EOR or LEO refill requires an LV bigger than EELV Heavy, approximately 50mT IMLEO.

EOR is a good option until cryogenic propellant transfer or bigger launch vehicles come along. Single launch is less complicated which is one of the better arguments for a larger launch vehicle. EELV Phase 1 would be the obvious candidate. The complexities of EOR could be mitigated by using the ISS as a staging point and launching the crew first.

EDIT: propellant transfer still requires EOR of course.
« Last Edit: 02/02/2010 11:47 pm by mmeijeri »
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Offline Robotbeat

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Re: L1/2 spacestation with depot
« Reply #111 on: 02/02/2010 11:53 pm »
To get crew to EML without EOR or LEO refill requires an LV bigger than EELV Heavy, approximately 50mT IMLEO.  Dragon and Dream Chaser don't have the habitable volume and life-support for a 6-day trip (each way) on their own.  So the CTV is an Orion-like 20mT through TLI.

The CTV could be as light as 16mT through TLI with an expendable hab module (e.g. Dragon + Sundancer), launched on two F9s.  That still puts the EDS slightly out of the range of Atlas V 551, and Dragon would be a bit short of the dV to push itself and Sundancer through ROI.

Dragon really needs at least twice as much propellant to play this role.  The tankage may not fit in the capsule, and it may be more appropriate to add another propulsion system in the expendable trunk.  This probably exceeds the performance capability of F9.  It may be able to go on Atlas V 402.
Falcon 9 heavy or Falcon 9 with a "Raptor" hydrolox upperstage (or a Falcon 9 heavy with "Raptor" hydrolox upperstage, giving you 45 tons to LEO) are viable alternatives.
Forget about LEO staging to an exoatmospheric CTV.  The propulsive braking required to return to LEO involves a round-trip dV of at least 7.5 km/s to EML1.  That makes the EDS considerably bigger than it would be for a heavier direct reentry CTV.
I _won't_ forget it. If you are using prop depots (and sep tugs), the exponent is broken up. It's not 7.5 km/s, it's 3.7km/s twice. There's a big difference. If using 311s isp propulsion for your exoatmospheric-only crew transport vehicle (would also be a depot/hab and/or a lander), that's a mass-fraction of 7 instead of 12. Almost twice as much. It means you can use a LEO commercial crew vehicle which is already developed, instead of paying billions extra for a new development, money that can be simply spent on propellant (which can help increase launch rates).
« Last Edit: 02/02/2010 11:54 pm by Robotbeat »
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Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #112 on: 02/02/2010 11:58 pm »
Almost twice as much. It means you can use a LEO commercial crew vehicle which is already developed, instead of paying billions extra for a new development, money that can be simply spent on propellant (which can help increase launch rates).

As you know I'm all for commercial propellant launches and SEP, but not to use LOX/LH2 for TLI seems wasteful to me. Why not rendez-vous with a cryogenic EDS in LEO? I can see why you would want to do this while you were waiting for an EDS to be developed on the basis of an existing upper stage. Or if your upper stage is very small like ECA, as was discussed on the man-rated Ariane thread. But not as a general solution.

But hey, if NASA wanted to fund it, I'd not be complaining. :)
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Offline Robotbeat

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Re: L1/2 spacestation with depot
« Reply #113 on: 02/03/2010 12:01 am »
Almost twice as much. It means you can use a LEO commercial crew vehicle which is already developed, instead of paying billions extra for a new development, money that can be simply spent on propellant (which can help increase launch rates).

As you know I'm all for commercial propellant launches and SEP, but not to use LOX/LH2 for TLI seems wasteful to me. Why not rendez-vous with a cryogenic EDS in LEO? I can see why you would want to do this while you were waiting for an EDS to be developed on the basis of an existing upper stage. Or if your upper stage is very small like ECA, as was discussed on the man-rated Ariane thread. But not as a general solution.

But hey, if NASA wanted to fund it, I'd not be complaining. :)
Good point about the hydrolox. You wouldn't use something with that low of an Isp. I chose a low Isp to highlight what a difference breaking up the exponent makes, something you can do with prop depots and SEP tugs.
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Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #114 on: 02/03/2010 12:06 am »
Ah, I see. Note that van Allen crossing tugs are still a while away, and they'd be necessary to make this efficient. Aerobraking would be another option, but that needs significant R&D too. I'd be worried about putting all that on the critical path, but eager to see it put on a technology development track. I like frequent small operational milestones. It does increase the risk that further development is terminated early or postponed because sponsors are happy with the initial capability, and that's not good. But then at least it would have been canceled after having delivered an operational capability instead of before it did as with Constellation.
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Offline butters

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Re: L1/2 spacestation with depot
« Reply #115 on: 02/03/2010 12:11 am »
So you need the station modules, the lander, the SEP tug, the crew transport vehicle, a big enough launch vehicle or cryogenic propellant tankers, storable propellant tankers, and MPLMs.  Piece of cake...
You'd want an incremental path towards this.

You could start with the lander itself, which could serve as a mini space station, depot and lander. Then you could add a hab. You could also do this in the reverse order.

The station is really only necessary for telescope servicing and such.  For the moon, all we need is a lander and propellant tankers in addition to the CTV.  The lander is light enough (and a one-time trip) to use chemical propulsion to get it to EML.  It would be nice to send the tankers (and also cargo landers) using SEP tugs.

Offline Robotbeat

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Re: L1/2 spacestation with depot
« Reply #116 on: 02/03/2010 01:06 am »
Ah, I see. Note that van Allen crossing tugs are still a while away, and they'd be necessary to make this efficient. ...

I'm not so sure that van Allen belt-crossing is that far away. From what I've read, it involves a thicker coating of radiation-hardening material, which impacts your specific power (not too bad, actually), but specific power isn't so critical at 1 AU from the Sun and if you have enough time and if you already have a quite healthy specific power. I am not convinced this is such a big problem. A radiation-hardened solar array could be demoed on the very first solar-electric tug.
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Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #117 on: 02/03/2010 01:11 am »
The station is really only necessary for telescope servicing and such.

You might be able to avoid it even for that if you added an optional robotic arm to the lander. Of course, there is no strict reason to avoid a space station since Bigelow modules appear to be close to being a reality. Either way, I'd like the lander to be the cis-lunar and later translunar equivalent of the Shuttle: a jack of all trades while still being a good lander. I'd be perfectly happy with NASA developing this beast in-house, as long as they only used TRL 9 technologies. Commercial players are a long way away from doing anything that is fully commercial beyond LEO and this approach would help them get into LEO faster.

There does not appear to be money for it in the foreseeable future however. Still, it's fun to speculate and fantasise.
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Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #118 on: 02/03/2010 01:16 am »
I'm not so sure that van Allen belt-crossing is that far away. From what I've read, it involves a thicker coating of radiation-hardening material, which impacts your specific power (not too bad, actually), but specific power isn't so critical at 1 AU from the Sun and if you have enough time and if you already have a quite healthy specific power. I am not convinced this is such a big problem. A radiation-hardened solar array could be demoed on the very first solar-electric tug.

There's apparently also a new self healing material that doesn't lose more than 20% of its performance after its initial pass through the van Allens. I'll dig up the link if you want. Stirling engines are apparently also a near term possibility. Note that even so the economics of SEP for LEO to L1/L2 are not obvious. Round trip times are high, which means you have a lot of capital costs. Beyond the Earth moon system they are highly plausible, especially for propellant.
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Offline A_M_Swallow

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Re: L1/2 spacestation with depot
« Reply #119 on: 02/03/2010 01:41 am »
The radiation hardness of the solar arrays can be tested using a mini tug.  The test tug could spend its time flying up and down through the Van Allen belts.  A mini tug with small solar panels can be launched on a Pegasus or Falcon 1.  There are several small ion engines, one of which may be suitable.

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