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.
...According to this article discussing Belbruno trajectories http://www.thespacereview.com/article/569/1QuoteThe 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.
Quote from: Archibald on 02/01/2010 06:27 am...According to this article discussing Belbruno trajectories http://www.thespacereview.com/article/569/1QuoteThe 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?
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.
Quote from: Robotbeat on 02/01/2010 11:49 pmQuote from: Archibald on 02/01/2010 06:27 am...According to this article discussing Belbruno trajectories http://www.thespacereview.com/article/569/1QuoteThe 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.
But I would suspect it would be time consuming trip.
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...
To get crew to EML without EOR or LEO refill requires an LV bigger than EELV Heavy, approximately 50mT IMLEO.
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.
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).
Quote from: Robotbeat on 02/02/2010 11:53 pmAlmost 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.
Quote from: butters on 02/02/2010 09:14 pmSo 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.
Ah, I see. Note that van Allen crossing tugs are still a while away, and they'd be necessary to make this efficient. ...
The station is really only necessary for telescope servicing and such.
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.