On a related note, isn't it also very difficult to bring a SEP craft to lunar orbit Moon using only its own power? Switching the PPE to a commercial launch brings many new issues.
Quote from: DreamyPickle on 02/27/2018 07:25 pmOn a related note, isn't it also very difficult to bring a SEP craft to lunar orbit Moon using only its own power? Switching the PPE to a commercial launch brings many new issues.It's certainly slower than using chemical propulsion as far as lunar-orbit insertion, but there's no rush. SMART-1 went as far as GTO on chemical propulsion and from there went electric.
Forty-two minutes after launch SMART-1 was placed into a geostationary transfer orbit, 742 x 36 016 km, inclined at 7° to the Equator.
The last firing of the EP before lunar capture was a thrust arc around the third lunar resonance, and ended on 14 October 2004. Apart from a 4 hour correction burn on 25 October, the EP remained inactive until lunar capture. Up to 26 October, and the 289th engine pulse, the SMART-1 EP system had cumulated a total on time of nearly 3650 hours, consumed about 59 kg of xenon and imparted to the spacecraft a velocity increment of approximately 2735 ms-1 (9850 kmh-1).
Much like the terrible idea of "Lagrange Gateways" that's been floated for years, now NASA pushes an even worse idea.
Why are "Lagrange Gateways" a terrible idea?
Looks like in the budget proposal from a couple weeks back the Deep Space Gateway has been renamed the "Lunar Orbital Platform", the propulsion module now has funding attached to it ($504 million next year, $2.7 billion over five years), and the targeted launch date is actually being moved up to 2022. It is also now is planned for launch on a commercial vehicle instead of on the EM-2 SLS flight.
Quote from: Propylox on 07/21/2017 03:09 am Much like the terrible idea of "Lagrange Gateways" that's been floated for years, now NASA pushes an even worse idea.Why are "Lagrange Gateways" a terrible idea?
Quote from: JacobLutz7 on 01/20/2018 06:23 pmOrion does not have enough propulsive capability to enter and return from LLO. Yes, that's true. It does have enough delta-V to leave LLO though. An EUS designed to last the three day journey to the Moon could do LLO insertion with Orion (as well as an LM on a separate mission).
Orion does not have enough propulsive capability to enter and return from LLO.
Orion doesn't have the delta-V to return from lower lunar orbits, ...
And SLS doesn't have anywhere near the launch rate to support a traditional crewed Mars mission architecture like DRM 5.0, so NASA will have to rely on an unproven, high-power electric transit stage (the Deep Space Transport) to get to Mars with fewer launches.
b) we've already been to the moon!
Of course, another rocket would need to place Orion in LLO for this to work.
You can do a Mars mission from LEO using only three SLS Block II launches (first launch carries Orion, Hab and Lander/MAV in re-entry fairing, second and third launches refuel SLS upper stage for TMI).
NASA's gateway plan requires a lot more launches than that.
Quote from: UltraViolet9 on 03/03/2018 07:46 pmOrion doesn't have the delta-V to return from lower lunar orbits, ...Yes it does. Orion has a delta-V of 1.2 km/s. That's sufficient for TEI from LLO. Of course, another rocket would need to place Orion in LLO for this to work.QuoteAnd SLS doesn't have anywhere near the launch rate to support a traditional crewed Mars mission architecture like DRM 5.0, so NASA will have to rely on an unproven, high-power electric transit stage (the Deep Space Transport) to get to Mars with fewer launches.Have you actually compared the number of SLS launches for both architectures? You can do a Mars mission from LEO using only three SLS Block II launches (first launch carries Orion, Hab and Lander/MAV in re-entry fairing, second and third launches refuel SLS upper stage for TMI). NASA's gateway plan requires a lot more launches than that.Quoteb) we've already been to the moon!We've also been to LEO, but we still keep going there. That's because its worthwhile to do so. Same with the Moon.
But we're using it's kissing cousin in DSG/LOP-G as a point solution band-aid to keep a deficient exploration architecture from falling apart.
Quote from: UltraViolet9 on 03/03/2018 07:46 pmOrion doesn't have the delta-V to return from lower lunar orbits, ...Yes it does. Orion has a delta-V of 1.2 km/s. That's sufficient for TEI from LLO. Of course, another rocket would need to place Orion in LLO for this to work.{snip}
Quote from: Steven Pietrobon on 03/04/2018 04:59 amQuote from: UltraViolet9 on 03/03/2018 07:46 pmOrion doesn't have the delta-V to return from lower lunar orbits, ...Yes it does. Orion has a delta-V of 1.2 km/s. That's sufficient for TEI from LLO. Of course, another rocket would need to place Orion in LLO for this to work.{snip}A depot in LLO could refuel the Orion's service module.
Quote from: A_M_Swallow on 03/04/2018 04:21 pmQuote from: Steven Pietrobon on 03/04/2018 04:59 amQuote from: UltraViolet9 on 03/03/2018 07:46 pmOrion doesn't have the delta-V to return from lower lunar orbits, ...Yes it does. Orion has a delta-V of 1.2 km/s. That's sufficient for TEI from LLO. Of course, another rocket would need to place Orion in LLO for this to work.{snip}A depot in LLO could refuel the Orion's service module.In theory yes, but adds another potential point of failure. Having crew stuck in LLO because of refuelling failure is not good outcome.
Round trip for lander is 5.5km/s for NRO compared to 3.7km/s for LLO so extra 1.8km/s. If DSG is already in place better to design lander to stage from.Best to wait a few years and see what comes out of robotic exploration. With ISRU lunar refuelling lander only needs to be capable of 2.7km/s. Can be LH LOX as boil off is not an issue over a day. The extra development costs of 5.5km/s lander compared to 2.7km/s would go long way to help pay for small ISRU plant.
Would that EDS also brake the group of spacecraft into Martian orbit, and return them later to Earth? Or would there have to be a Earth Return Stage(s), waiting there for them to send the Orion and Habitat back?
Quote from: TrevorMonty on 03/04/2018 05:43 pmQuote from: A_M_Swallow on 03/04/2018 04:21 pmQuote from: Steven Pietrobon on 03/04/2018 04:59 amQuote from: UltraViolet9 on 03/03/2018 07:46 pmOrion doesn't have the delta-V to return from lower lunar orbits, ...Yes it does. Orion has a delta-V of 1.2 km/s. That's sufficient for TEI from LLO. Of course, another rocket would need to place Orion in LLO for this to work.{snip}A depot in LLO could refuel the Orion's service module.In theory yes, but adds another potential point of failure. Having crew stuck in LLO because of refuelling failure is not good outcome.You could always refuel in NRHO. Orion would use about 3300 kg of propellant to get into NRHO, be topped off to go to LLO and back (~1400-1500 m/s). It might be at a slight ~100 m/s deficit compared to a benchmark 100 km altitude circular orbit. Then it would just have to be fueled with about 2500 kg of propellant for the trip back to earth. Alternatively, it could be directed back to earth(TEI from LLO is about the same as LLO to NRHO(~750-800 m/s).Or you could launch something else in the USA with a docking port to attach to the Orion. A lot of things would work to make up the modest 500 m/s deficit that Orion has to enter LLO and return to earth. A second SM with a docking port kit, a lunar descent stage equivalent in performence to th LEM descent module or even a ~8 mT chemical propulsion comsat with about 4200 kg of propellant(that it would need for GEO circularization - ~1.6 km/s, stationkeeping at 50 m/s per year anyway). The Block 1B is so overpowered for putting Orion alone into LLO that all kinds of not necessarily efficient schemes could work. But what is the point with LLO really? It adds 1000 m/s of requirements on the Orion(vs NRHO), but subtracts 1000 m/s of requirements from the lander (vs staging at NRHO). The lander can be smaller and lighter compared to Orion that has to re-enter and support crew for longer durations and thus it could very well take less fuel to move the lander an extra 1 km/s vs move Orion an extra 1 km/s