There's a lot of discussion elsewhere about whether or not SLS should be canceled.
This thread is about something less commonly discussed: what to replace SLS with.
Canceling SLS would mean canceling Orion. There is no replacement.
If the U.S. Government doesn't have enough demand to merit owning and operating their own HLV, then there is no need to replace it with another U.S. Government-owned transportation system.Which means the U.S. Government will rely on the U.S. aerospace sector to take care of it's needs - something that the U.S. aerospace sector should be more than capable of doing using their own transportation systems.
Quote from: edkyle99 on 11/28/2016 12:34 amCanceling SLS would mean canceling Orion. There is no replacement.There are four commercial super-heavy US launch vehicles under development:-Vulcan Heavy-New Glenn-Falcon Heavy-ITSWikipedia says Orion + Service Module is about 25 tonnes and 5m diameter. That should be well within the capabilities of all four launchers unless there's a problematic detail such as launch vibrations. Several of those launch vehicles have a lot of development left but Falcon Heavy is almost ready. Why do you say that canceling SLS implies canceling Orion?Orion was originally a Moon capsule and AFAICT would do OK at that role. Orion doesn't seem very useful however for the Mars program of record. Therefore my two cents on Orion is we should cancel it if we continue with the Mars destination but keep Orion if we switch to the Moon.It appears that the first three vehicles have similar performance: they’ll all be able to send about 20 tonnes to GTO. (Sources: https://twitter.com/torybruno/status/595628488410963970, http://forum.nasaspaceflight.com/index.php?topic=41146.msg1589576#msg1589576, http://www.spacex.com/falcon-heavy.) It seems unlikely that all three will get built but ISTM at least two vehicles of this class will be, especially if NASA throws a little funding and demand at them. New Glenn and Falcon Heavy seem like the most likely of the four to actually be built so maybe NASA should baseline them? Volume-wise anything that Falcon Heavy can launch New Glenn presumably can too (because of its almost 2x diameter). Which of the two is limiting mass-wise probably depends on target orbit, reusability choices, and whether Falcon Heavy gets cross-feed.Quote from: Coastal Ron on 11/28/2016 12:49 amIf the U.S. Government doesn't have enough demand to merit owning and operating their own HLV, then there is no need to replace it with another U.S. Government-owned transportation system.Which means the U.S. Government will rely on the U.S. aerospace sector to take care of it's needs - something that the U.S. aerospace sector should be more than capable of doing using their own transportation systems.I completely agree -- a replacement government HLV would not be sufficiently better than SLS to justify starting over. The question is the details of what to buy and how. Exploration hardware is quantized so NASA needs some mass and volume specifications to design to. If NASA designs to a single launch vehicle NASA won't benefit from competition. So what launchers should NASA design for? (Or really, what specifications?)
Orion can/would make an excellent Cislunar space 'Mothership'. Heh - rather like 'Apollo on Steroids'.
Quote from: MATTBLAK on 11/28/2016 04:11 amOrion can/would make an excellent Cislunar space 'Mothership'. Heh - rather like 'Apollo on Steroids'. To me it does not look like Apollo on steroids. More like an aged overweight Apollo.SLS might have some reason to exist. Orion does not.
There is no need to cancel Orion as it could be launched with less powerful launchers.
And actually cancelling SLS would free up more money to keep it.
But assuming we are actually serious about going to mars, where the money needs to go is all of the payloads that are not being developed right now that will be needed for that.
The path we are on right now will see SLS completed with nothing useful for it to launch.
So what launchers should NASA design for? (Or really, what specifications?)
The only two LVs capable of delivering Orion to BLEO would be SLS and 2x Vulcan (distributed launch). With FH and NG it would just be a very expensive LEO taxi.