Author Topic: Hypothetical scenario about SpaceX lunar tourism (Read 3686 times)

Pipcard · « **on:** 03/04/2017 07:29 pm »

Note: this is about a hypothetical scenario. This is not about what SpaceX is likely to do.

There are two assumptions in this scenario:

- the Dragon can't do precise propulsive landings reliably from BEO re-entry speeds (and has to splash down), but can still land precisely from LEO

- The ITS is not being developed (yet) in this universe, and smaller ambitions of cislunar tourism (flybys and landings) are being promoted instead. A reusable lunar lander that travels between a Lagrange point and the lunar surface was developed, but that is not the point of this.

This scenario might seem contrived, but would it be better if

1. there was a series of reusable vehicles, i.e. Earth-LEO, LEO-L1/L2, L1/L2-Moon
(the Moon lander and LEO-L1/L2 vehicles can even share common components)

Quote from: moralec

If you want to have tourists going to the moon and back on a regular basis, while maximizing safety and minimizing costs, it doesn't make sense to think about a single Apollo-like system around the Drago capsule, handling both the transportation from earth to the moon and the landings. Carrying a Dragon capsule with a heat shield all the way to the moon for example, is unnecessary. You could have instead several specialized pieces of infrastructure (one of them being the Dragon spacecraft), each handling a different part of the trip.

https://forum.nasaspaceflight.com/index.php?topic=34867.msg1210805#msg1210805

because

Quote from: InfraNut2

Reuse is the key to make cis-lunar space tourism widespread instead of rare

https://forum.nasaspaceflight.com/index.php?topic=34867.msg1211075#msg1211075

Quote from: Elmar Moelzer

It would increase the initial cost, but could be cheaper and more flexible in the long term.

https://forum.nasaspaceflight.com/index.php?topic=34867.msg1210130#msg1210130

or

2. only the Dragon capsule was used (remember that it is assumed that it could only splash down from BEO)

because

- you absolutely need a means of re-entering (because there is the risk that rendezvous with the Dragon in LEO that is supposed to take you back to Earth's surface might fail in the first option)

- it minimizes development costs.

- you can take advantage of aerobraking instead of propulsively braking into LEO, thus minimizing the number of launches (to send propellant) and complexity of each trip

(for both cases, it is also assumed that the development costs of large-scale solar electric propulsion are not worth it, so please do not say "just use a SEP tug to ship propellant")

rakaydos · « **Reply #1 on:** 03/05/2017 06:20 pm »

I'd say Dragon to L1/L2 and back, with aerocapture to LEO, go around for another pass without the trunk solar panels, and land.

Roy_H · « **Reply #2 on:** 03/06/2017 06:20 pm »

Multiple steps, although more capital intensive, does have the long term reduction in costs. It also has the advantage of being a more interesting tourist trip. Transferring to different vehicles with hopefully more room to move around in and amenities would be less boring and break up the travel into bite-sized chunks.

Jim · « **Reply #3 on:** 03/06/2017 06:49 pm »

Quote from: Pipcard on 03/04/2017 07:29 pm

- you can take advantage of aerobraking instead of propulsively braking into LEO, thus minimizing the number of launches (to send propellant) and complexity of each trip

You mean aerocapture?

moralec · « **Reply #4 on:** 03/06/2017 07:29 pm »

Its really all about the volume and frequency you are expecting to have. Are you considering ferrying hundreds/thousands of tourists a year, or just a few millionaires every now and then?

If you are going to fly very infrequently, better to use the systems you already have and not spend time, money and effort developing new things.

If you are going for volume, however, the more sustainable option is definitely the way to go:
- As I said above it doesn't make much sense to carry the heat shield, entry suits and parachutes all the way around the moon.
- By having multiple vehicles you can design each with a single objective/with a unique environment in mind (The lunar landers can be built with very light materials, the reentry capsule can be sturdy, etc)
- By making the trip more conformable (having proper bathrooms, privacy, etc), you can tap into a broader market of potential tourists (not only the space obsessed niche) and Maximise network effects (more e adopters that recommend the "pleasant" experience to others)
- You could also offer a wider variety of trips. For example, trips to LEO, moon flybys, moon landing, etc
- Also you can offer longer duration flights (spending a full a week on a dragon is already pushing it. Can't imagine someone wanting to spend a full month trapped on it)

mikelepage · « **Reply #5 on:** 03/12/2017 03:17 pm »

I think there will have been some serious numbers of people going around the moon for tourist flybys (1000+) before any dedicated (heat shield-lacking) craft will be built specifically for the trans-lunar injection part of this "tourist trail". Having said that, I can imagine one small modification that would allow maybe 4 people to go at a time. Dragon V2 + a single BEAM (variant) module.

Falcon Heavy can put ~15 metric ton payload into TLI with Dragon V2 onboard (according to anonymous reddit calculator, but sounds about right). Dragon V2 fully loaded was estimated at 8.9 metric tons (also according to anonymous reddit calculator, but also sounds about right). BEAM (skeleton version launched to ISS) was 1.4 metric tons, so it seems there is margin for any inflatable module to be much better equiped (to incorporate a cupola at the far end of the BEAM for example).

The other thing you would need is a method which would allow the Dragon to dock to a BEAM module stored in its trunk, perhaps with a miniature Canadarm type robot? Or perhaps following TLI, pre-inflation, the BEAM module could attach itself to the second stage, and the Dragon V2 could pull forward, flip, and come back to dock with it that way. If it isn't successful, you've got 4 people crammed in Dragon for a week, but thats just uncomfortable, not mission-ending.

---
Had an afterthought about what happens to that BEAM module at the end of the mission. Obviously, only the Dragon V2 is coming back, and the trunk will burn up in the atmosphere, but the BEAM doesn't need to. You could sell this to your customers as the ultimate time capsule. If you planned to undock from the BEAM and make adjustment burns a number of hours before re-entry, you could plan to have the BEAM not enter the atmosphere, and actually be on a trajectory where it will eventually re-encounter the moon and be slingshot into interplanetary space. I can think of a few cool biology experiments I'd want to do if I got the chance to send a pressure vessel into heliocentric orbit.