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Re:Elon Musk unveils first tourist for SpaceX 'Moon loop' by sschueller on Tuesday September 18, 2018 @05:30AM (#18013757)
Add parachutes and dump them in the sea.
Re:Elon Musk unveils first tourist for SpaceX 'Moon loop' by olex on Tuesday September 18, 2018 @05:37AM (#18013789)
That actually adds more mass than the extra fuel required for propulsive landing. And significant refurbishment of engines is needed after they've contacted salt water.
Re:Elon Musk unveils first tourist for SpaceX 'Moon loop' by dexen on Tuesday September 18, 2018 @06:13AM (#18013938)
We were using parachutes for the Space Shuttle SRBs, but there are certain important distinctions - the SRBs were, to a first approximation, "big dumb pipes", and had much less of a problem with saltwater damage due to water landing needed to cushion the impact. There were 3 parachutes, for a total of 3x 990kg [1] for the SRB's empty mass of 91'000kg. While Falcon Heavy's first stage is lighter (25'600 kg empty, each [2]), you would need disproportionately larger parachute size to achieve soft landing on the ground as opposed to SRB's water landing, to avoid salt water damage. And to possibly handle passenger flights.

Off of the top of my head, with parachute landing you add mass because both:

- the large parachutes are quite heavy themselves as above (add some overhead for covers and support installation; I can't find any numbers)

- needs increased structural integrity to handle the tug during deployment and the much faster touch-down on landing; with propulsive landing you can essentially touchdown at 0/0/0 vertical/horizontal/angular velocities, as soon as you nail down the math of flight characteristics and engine control

- possibly some sort of reaction control, to achieve proper deployment attitude

- probably a smaller drogue chute(s) to handle supersonic flight, with all the complexity it adds

Moreover, using chutes:

- completely prevents RTL flights

- complicates abort modes; you'd need to dump fuel and oxidizer quick (without mixing and igniting, good luck) to be able to rely on the chutes alone.

However I guess the overriding concern for Musk was quick turn-around. With a parachute landing you have less control over the touchdown point [3]; the logistics of recovery, refurbishment and relaunch become much more involved, possibly spanning an ocean [4]. And with longer turn-around you need more flight hardware, and more ground support, to handle given amount of orbital or surface-to-surface traffic. Call it reducing the capex by going for somewhat costlier option that ensures much higher flight hardware utilization.

Lastly, using parachutes would create an image of low reliability; it's not something we would consider as to be routinely performed by commercial passenger flights. You don't want to ship passengers to "somewhere near your destination"; you want to deliver them to the airport, right next to the jet bridge (call it rocket bridge?) and promptly usher them to the passenger terminal.

Yes, yes, the routine BFR passenger travel is coming.

[1] https://en.wikipedia.org/wiki/Space_Shuttle_Solid_Rocket_Boo...

[2] http://www.spaceflight101.net/falcon-9-v11.html

[3] Gemini-style Rogalo wing would help, if it could be scaled. See https://i.pinimg.com/564x/b0/84/87/b08487e18f16402e4867981ff... and https://vintagespace.files.wordpress.com/2011/12/rogallo-win... Not as preposterous as it may seem, given that Buran's side-boosters were to glide to landing on deployable wings; see http://www.buran.ru/images/jpg/gk175-5.jpg

[4] you could bulk up the 1st stage enough to let it coast suborbitally all the way around globe to RTL, but that's another matter - and again uses up valuable fuel, and you run up against the rocket equation pretty quickly.

Re:Elon Musk unveils first tourist for SpaceX 'Moon loop' by adrianN on Tuesday September 18, 2018 @05:41AM (#18013810)
Parachutes don't work very well on Mars. Salt water kills delicate machines. Parachutes need very sturdy (and heavy) rockets.
Re:Elon Musk unveils first tourist for SpaceX 'Moon loop' by gliptic on Tuesday September 18, 2018 @06:26AM (#18013990)
If you knew history, you'd know this has been tried before. The shuttle boosters did this; they barely saved any money after refurbishing.

SpaceX tried it too, but had significant problems even re-entering without the rocket ripping apart, not even getting to the problems of recovering and refurbishing salt-water damaged hardware.

This kind of attitude might have made more sense before SpaceX had demonstrated it was possible. After showing how the technology can be further refined for full and rapid reuse, and landing on Mars, it just reads as ignorant or intentionally misleading.

Re:Elon Musk unveils first tourist for SpaceX 'Moon loop' by C14L on Tuesday September 18, 2018 @05:39AM (#18013806)
1. No sea on Mars.

2. Turnover of 24 hours would become impossible.

3. Structural stress so 10 re-flights would become unlikely.