Future of spaceflight

[Nesti (Mark)]

***I've added this note after the thread started: I've read many a post of what the future of space flight may be, or look like. I wanted to start this thread so that we could discuss space flight in a real physics related manner. To look at ideas and concepts which are doable and ones which are not possible...and why. You might be surprised that what's pushed in mainstream media (TV Docs etc) may not even be a realistic approach to space travel***


With the shuttle's service life almost at an end, I wonder what the next generation of vehicle - after the next phase of Russian Soyuz assistance - will look like; what it will be?!

Unfortunately it's not just costly to take payload to orbit, it's also costly to take anything you want to reuse up to orbit and back again. The additional size and mass of the vehicle which needs to be lifted and needs to reenter the atmosphere just adds-up and the fuel loads become obscene...and you cannot skimp on quality either.

I have always felt that lifting mass to L.E.O. (Low Earth Orbit) is more suited to expendable technology, rather than reusable. Reusable technologies are lifed and require scheduled service/repair cycles. One-off expendable technologies are often lighter and simpler in design, and if the Apollo program learned anything, it was that weight and design simplicity is everything in spaceflight. Even though the Apollo program utilised vehicles which were entirely expendable, perhaps future flights across to the moon and back might best suit a reusable (serviceable/repairable) vehicles.

Programs like the X-33 and X-34 were doomed before they even got off the ground, no matter how much romance was attached the the concepts and the overall look. The design philosophy was more befitting a maintenance/supply/repair contractors' dream than anything else...much the same as the space shuttle believe it or not!

So, what do you think will be;

1. The next heavy lifter of payload to L.E.O. ?
2. The next moon mission vehicle ?

(I've deliberately left out [safe return] Mars missions, as we are nowhere near ready to undertake such a journey)

[supernova1965 (Warren)]

Originally Posted by Nesti

1. The next heavy lifter of payload to L.E.O. ?

I think that we will eventually get SPACE ELEVATORS for payload to L.E.O

http://www.howstuffworks.com/space-elevator.htm

[michaellxv (Michael)]

Lifting to L.E.O. and travelling around space are 2 different problems and would be best served by specific solutions.

Comercial projects like Virgin Galactic will be able to take care of the L.E.O lifting.

Dedicated Space vehicles can shuttle back and forth between Earth and Moon. Being permanently in space and only needing to be lifted once they won't be limited in design to fitting inside the nose cone of a traditional rocket.

Ideally this vehicle would be capable of landing on the moon without the need for a separate lunar landing vehicle.

[Nesti (Mark)]

Originally Posted by supernova1965

I think that we will eventually get SPACE ELEVATORS for payload to L.E.O

Space Elevators are a nice idea but, when you apply weather, precision in rendezvous (especially timing constraints), loads on cabling, and the sheer complexity of the design itself , is the Space Elevator really viable?!

The concept of a Space Elevator on the Moon is fantastic, as there is no atmosphere to contend with, 1/6th gravity (1/6th cable loading) and a much slower orbital speed means a lower orbital mass centre and less altitude to a lunar orbit.

[Nesti (Mark)]

Originally Posted by michaellxv

Lifting to L.E.O. and travelling around space are 2 different problems and would be best served by specific solutions.

Comercial projects like Virgin Galactic will be able to take care of the L.E.O lifting.

Dedicated Space vehicles can shuttle back and forth between Earth and Moon. Being permanently in space and only needing to be lifted once they won't be limited in design to fitting inside the nose cone of a traditional rocket.

Ideally this vehicle would be capable of landing on the moon without the need for a separate lunar landing vehicle.

I agree that private entities, not just government agencies, would be needed for successful space travel in the future.

A dedicated spacecraft would still require servicing and repairs. There's no way you could do intermediate or depot level maintenance in orbit; so they've got to come down at some point and that would depend upon the servicing cycle (number of operational hours versus reliability). This would mean re-entry, and that means specific design philosophy (heat shields and aerodynamic concerns), which of course means additional weight.

The contest to find the 'Mode' of landing on the moon (Lunar Orbit Rendezvous or Direct Assent) and returning to the Earth by using a single vehicle or two dedicated vehicles was fought and won back in the late 50's. In the end, the design physics called for both Lunar Orbit Rendezvous and Earth Orbit Rendezvous.

It all comes back to a very simple physics principle; for every kilo of additional mass you take to the lunar surface and bring back to Lunar Orbit, add 5 kilos of propellant. Add 6-7 kilos of propellant if you want it to come back to Earth Orbit (these figures do not include the initial lift to Earth orbit, which becomes extreme). So if the combined vehicles' dry-weight is 20% greater, then the all-up weight will be double that of a combined two vehicle solution. There's not much chance of using a single 'multitask' vehicle; it becomes too massive to do the job, and additional mass means extensive trade-offs in payload. I haven't introduced additional structural mass or larger power-plant for a single vehicle, but that would have to increase the single vehicle design by at least 40-50%, not a mere 20%.

If it were possible to construct a single vehicle, which traveled from Earth Orbit to the surface of the moon and returned to Earth Orbit, and that it was a mere 20% heavier, would require a Booster Rocket on the launch pad at least twice the size of the Saturn V.

I didn't want to introduce Mars, but just to give you an idea of the complexity and real world contingency plans that would be required, I wouldn't be surprised if going to another planet in our system called for at least 6 separate unmanned service vehicles to make the journey first. The construction of an orbital station, at least two Mars escape vehicles on the planet itself and two habitat stations. Then there's fuel, water and food depots, a maintenance workshop, vehicles for mobility, a medical surgery...the list is endless!

The reality of space travel becomes apparent when you realise that every single leg of the journey requires a dedicated, specifically designed technology, and then that technology must fit-in with the whole design...so a vehicle that lands on Mars cannot land on Titan or even our own moon.

[michaellxv (Michael)]

I agree heavy servicing in space is not practical yet. Surely a design which gets even only 2 trips out of a spaceship is an improvement on the single trip of the Apollo design. Even this won't be easy as just resupply of food and water in space is not trivial let alone oxygen and rocket fuel. But, if we are serious about regular space travel these are the type of obstacles to be overcome.

It would be easy to say it's too hard and that the physics is against us, but I think there is a solution out there. It may just be that we need to keep incrementally building in space as has been done since the begining.

[Nesti (Mark)]

Originally Posted by michaellxv

I agree heavy servicing in space is not practical yet. Surely a design which gets even only 2 trips out of a spaceship is an improvement on the single trip of the Apollo design. Even this won't be easy as just resupply of food and water in space is not trivial let alone oxygen and rocket fuel. But, if we are serious about regular space travel these are the type of obstacles to be overcome.

It would be easy to say it's too hard and that the physics is against us, but I think there is a solution out there. It may just be that we need to keep incrementally building in space as has been done since the beginning.

Actually, I believe that a we have enough reliability these days to keep a vehicle in continuous service for a full year. So a vehicle designed only to shuttle crew and stores from Earth Orbit to Lunar Orbit and back could run non-stop for a full year and then it becomes expendable...no servicing required.

A Lunar Orbit shuttle to the surface could have two options. The first option is to use an expendable descent stage but have a reusable ascent stage, or, have a reusable single vehicle. In this scenario, the second option, although heavier and fuel thirsty, has the greatest degree or reliability in that an ascent and decent two vehicle option are a mated pair, and must perform flawlessly...if decent stages are expendable after each use, there's no telling if the next decent stage will be reliable as it has not been tested as a mated pair to the reusable ascent stage. So in this case the safest option is to go with engine reliability and trade-off payload to and from the surface.

There is an alternative appearing here; make technology extremely reliable, but once a service life has been reached, that component (vehicle) becomes expendable...there is no servicing schedule! The key is to keep machines continually in service as they tend to fail when they stop-start all the time. Aircraft are never more reliable than when they are flown day-n-night and better still turned-around while still running (hot-refuel and turn-around).

The Booster Rocket from Earth to Earth Orbit is of course a separate and big issue.

[Karls48 (Karl)]

To my way of thinking what is required is three stage design, compromising of number of Earth based lift rockets, Moon shuttle that would carry payloads to the Moon orbit and at least two Moon landlers that would remain in Moons orbit. The Moon shuttle would be assembled in the space similar to the Space station. It would be probably most expensive solution but necessary if frequent travel to the Moon is anticipated. May I add that unless there is a burning military, political or economical need – not much is going to happen regarding space travel in foreseeable future.

[renormalised (Carl)]

I'd like to contribute to this thread but at present I don't have the time (big assignment). However I will say this...if we want to expand into the solar system, or even have regular Earth-Moon transportation and commerce, we're going to have to develop far better technologies than using what are nothing more than glorified fireworks. This insistence on using what is basically 900 year old technology will keep us in LEO (just barely) and that will be the end of it. If you want to make lift to LEO/GEO etc, cheaper and to allow us to move out into the solar system, we need means of propulsion far better than what we have or are considering of using, to do the job.

[Nesti (Mark)]

Originally Posted by Karls48

May I add that unless there is a burning military, political or economical need – not much is going to happen regarding space travel in foreseeable future.

You are absolutely correct. I'll go you one better; that the passion for space flight will diminish as two things happen.

1. The baby boomers die-off. X Generation are mildly interested, Y Generation will be into it so long as someone else does all the hard work and that their Play Station and X-Box can come along too.

2. As global economics worsens (can't see an end to that). Nuff said there.

Unfortunately, I cannot see much more than a spark of interest throughout the general public, let alone a space-race flame. Sad, but true.

[dalemadison]

Except for the Chinese. They will take their time but be in space while the western worlds space programs fight the politics and costs.

[TrevorW]

Aircraft carrier size derigible at 50000 feet then rocket boosted scram jet or similar to LEO,

ISS turned into a space dock where lunar orbiters and landers constructed

Lunar surface mining ore recovered by rail gun launch to LEO where captured and processed in orbiting refineries

[AJohnston (Angus)]

Does anyone know what's happening with the orion spacecraft?
It was looking pretty exciting for a while, but last I heard (wikipedia) the US government had cancelled it.
Does anyone know of future US manned space plans/what's going to happen to the iss when the shuttle retires in this case?

[renormalised (Carl)]

You know what type of propulsion system is needed...gravitomagnetic (the good ol' "anti-gravity" drive). Get these systems up and running and you won't have to worry about expendable rocket stages, or throw weights of rockets, carrying capacities etc etc. You could lift 100 ton into orbit for about the same price as it weighs and it'd get there just as quick or quicker than by a rocket. And a lot safer too. You could lift 10,000 ton into orbit, if you wanted to. No rocket could ever do that. All we need is a reliable and powerful power source to power the drive system.

What's needed is for the engineers and scientists to stop stuffing around with what is essentially 900 year old technology and start to think beyond the box. Then push for the funding to make things happen.

[Nesti (Mark)]

Originally Posted by TrevorW

Aircraft carrier size derigible at 50000 feet then rocket boosted scram jet or similar to LEO,

That's a very popular and intuitive idea, but alas, it's horizontal velocity that's needed and dropping boosters from 50,000ft provides little assistance.

The best so far seems to be 5km long underground tunnels filled with Helium and a 55-60 deg ramp at the end. This allows for an initial boost to mach 3 within a thin atmosphere. Maglev rails with boosters are proposed for the 'Dolly Launch'.