ShuttleA. How realistic is it? Anything better?

[Sky Captain]

What if we give shuttleA a nuclear lightbulb engines, ISP could be somewhere 25000 - 30000 m/s. I think this is the engine type shuttle A supposedly uses. To make shuttle A more realistic it would probably need to lower ISP from 40 000 to 30 000, also remove fixed main and hover engines and go with 4 gimballed engines for ease of flying and reduce thrust to the point it can only barely take off from the Moon with full load. Also nuclear lightbuld engine subsystem simulation would be neat.

 

[the.punk]

Hey what is with the Merlin Transporter?
[ame="http://www.orbithangar.com/searchid.php?ID=2234"]Merlin Transporter[/ame]
It looks realy nice.

 

[Urwumpe]

Even 65000 m/s are in the range of potentially realistic engines. The Black Dart engine uses only a limited amount of Handwavium, and that mostly in the injector design. The fusion processes, which I handwaved as power source of the main and hover engines, are actually even less effective as the current theoretical calculations for them - I selected a far higher amount of missed collisions, than we have in current tokamaks.

That is not the problem - the problem is, that all such designs can not be build. The Black Dart engine is mathematically sound, but assumes materials which we don't have. We could have them, that is not impossible. But I can't tell how a material with the handwaved properties looks like or where you can get it. I invented the material properties for filling gaps.

The same you have currently in any nuclear rocket engine design. Even NTRs contain assumptions, which are not always fitting with ground test data. But that does not make NTRs unrealistic - they are a reality already.

But a really built NTR would look different to the concepts you see in NASA publications or sci-fi literature. Not from the general shape - this would stay. But many small details inside and outside would have to vary and the performance figures would have to differ, to the worse or to the better.

 

[ar81]

Hey what is with the Merlin Transporter?
http://www.orbithangar.com/searchid.php?ID=2234
It looks realy nice.

You may use it with this
[ame="http://www.orbithangar.com/searchid.php?ID=3214"]Merlin 1.2 code scenario generator[/ame]
It will generate the code you need to add it to a scenario.
You may need to copy the code into your scenario.

Merlin is like a neat Shuttle-A.

 

[Clavius0712]

I doubt there would be any colonization effort around Jupiter at all. Which doesn't doom the prospect of a mission to Jupiter, it just says that missions will primarily be exploration and science missions, and that you probably won't see any permanent settlement larger than an ISS-sized research center.

A fair point but for the purposes of the simulation I was just trying to think of a date when such bases might be possible. 2061 is probably too optimistic but is sufficiently far off for us to consider novel spaceship designs such as fusion etc.

But for best realism, you'd have lander/launchers for the moons, which would dock with an inter-moon shuttle that would never touch the ground. The shuttle would also dock with your Earth-Jupiter ferry. At the Earth end, the ferry would dock with surface-to-orbit winged shuttles.

This could be just as fun if not more so for Orbiter. If each major moon has the equivalent of an ISS acting as orbital terminus for craft from the surface as well as craft from Earth or other Jovian moons, that's fine by me in terms of scenario design.

 

[Andy44]

Wow, looking at the info for the nuclear lightbulb, that sounds like a great idea. And somewhere I read that this thing has been prototyped and tested, at least the reactor part. Of course, a nuclear-powered Shuttle A is going to look alot different than what we're used to. And while we can envision lightweight gimbals for the engines, the shielding for four gimbal-mounted nuclear reactors is likely to be pretty heavy, not to mention problematic for the cargo modules and ground crews!

(BTW: Colonies around Saturn would make more sense than Jupiter. Shallower gravity well and less radiation. IMO.)

 

[Zatnikitelman]

Why not use a single reactor feeding four gimballed nozzles? One area of shielding versus four.

 

[Hielor]

Why not use a single reactor feeding four gimballed nozzles? One area of shielding versus four.

I was thinking about that too, but I think that could cause other issues:

-Single point of failure.
-The piping for the exhaust would have to be made of handwavium, I think....

 

[Andy44]

-The piping for the exhaust would have to be made of handwavium, I think....

Yeah, I'd think so! Even if you could deal with the heat, you'd lose thrust along the way, I think. The Rolls Royce Pegasus jet used in the Harrier has to deal with ducting the hot turbine exhaust off to either side. Ducting exhaust creates backpressures and you lose heat along the way to conduction and radiation.

 

[Hielor]

Wow, looking at the info for the nuclear lightbulb, that sounds like a great idea. And somewhere I read that this thing has been prototyped and tested, at least the reactor part. Of course, a nuclear-powered Shuttle A is going to look alot different than what we're used to. And while we can envision lightweight gimbals for the engines, the shielding for four gimbal-mounted nuclear reactors is likely to be pretty heavy, not to mention problematic for the cargo modules and ground crews!

(BTW: Colonies around Saturn would make more sense than Jupiter. Shallower gravity well and less radiation. IMO.)

Where's a good place to get actual information about the nuclear lightbulb? I read the "Liberty Ship" article, but I couldn't see that it was backing itself up with facts, and that presented a T/W ratio for the engines of only 10...I would think it would be much higher, given that modern rocket engines have T/W ratios in the 70s?

 

[Andy44]

I just googled around a bit. Don't know what's accurate. projectrho.com talks about it a little.

---------- Post added at 07:56 PM ---------- Previous post was at 07:18 PM ----------

BTW, according to projectrho, the nuclear lightbulb (NTR gas core/closed) has a thrust to weight ratio less than one, which is bad for a lander, even on the Moon, where the weight is decreased by 5/6. Increased gravity losses.

But I'm not sure what to believe about this system.

 

[Hielor]

I just googled around a bit. Don't know what's accurate. projectrho.com talks about it a little.

---------- Post added at 07:56 PM ---------- Previous post was at 07:18 PM ----------

BTW, according to projectrho, the nuclear lightbulb (NTR gas core/closed) has a thrust to weight ratio less than one, which is bad for a lander, even on the Moon, where the weight is decreased by 5/6. Increased gravity losses.

But I'm not sure what to believe about this system.

I've been kicking around thoughts of taking what's been mentioned in this thread and actually implementing it, but I wouldn't want to do engines without having any idea what the actual parameters would be.

Plus, I'm really not confident that i'd be able to do the ship justice

 

[Clavius0712]

I've been kicking around thoughts of taking what's been mentioned in this thread and actually implementing it, but I wouldn't want to do engines without having any idea what the actual parameters would be.

Plus, I'm really not confident that i'd be able to do the ship justice

If you decide to have a go at it, would it be possible to have a "descent hold" autopilot? Even a manual "descent rate" text entry box would do. I just need some way of precisely telling the ship how many m/s to descend at so I can do all those beautiful pad landings I've mastered with the XR2.

 

[Sky Captain]

I read about the Liberty ship, it seems to me a bit far fetched. I have doubts whether current materials technology is up to the task of managing 80 GW of thermal power in an engine smaller than school bus.

However for lander intended to operate on the Moon this kind of engine might be plausible especially if it`s supposed to be set in the middle of 21 st century with some advancements in materials technology. Anyway this is only engine type I`m aware of that dos not spew radioactive exhaust and has enough thrust and ISP to plausibly propel a shuttle A like craft that can land on the Moon and also fly short interplanetary flights.

 

[Koriel]

Just recently got back in Orbiter and have been once again playing with the shuttle A.

Been basically making runs between Shado Base and Brighton Beach.
Originally I used the AUX thruster a great deal but I have found they really are not needed.

What is needed.
4 MFD's on any ship really.
The Arrive MFD and Camera MFD.
Arrive I use the anti grav function as it allows for controlled assents and decents, (there really is no reason to hover)
And the camera MFD for landing (basically looking down so you can eyeball the pad and make small changes with laterals).
With those 2 and the other standard MFD's in orbiter you can fly a ship and land it with no windows.

As far as landing the shuttle A.
First when you decelerate turn the ship around and use the main thrusters.
Use the Vertical Speed function when you come out of orbit too keep it controled.
Keep in mind you really don't have to decelerate till 300 km @ the earliest (you can get even closer depending on how quick you are.) with the shuttle A (as others have said rather strong engines)

Basically come in about 200 km above the base by slowly reducing your speed. When you are moving about 5 m/s you can use laterals for a vertical landing.

There is more but basically you can't think like your flying a plane

 

[Hielor]

Arrive I use the anti grav function as it allows for controlled assents and decents, (there really is no reason to hover)

Er......yeah, cause that's realistic.

And the camera MFD for landing (basically looking down so you can eyeball the pad and make small changes with laterals).

Don't even need this--the built-in VTOL mfd does that just fine.

 

[Andy44]

Er......yeah, cause that's realistic.

If you try it you'll see that it is realistic. It just adjusts your hovers so that you can control your vertical speed directly with the hover throttles.

It has nothing to do with actual antigravity; it just makes it feel like antigravity to the pilot. Similar to the Flying Bedstead's gimbaled jet engine.

This business of an easier altitude ans vertical speed control has been solved by both the old Arrive MFD and computerex's AutoHover MFD. The former has that nice auto-throttle feature, while the latter allows you to use main engines for hovering with tail-sitters. A combination of both would be cool.

 

[Hielor]

If you try it you'll see that it is realistic. It just adjusts your hovers so that you can control your vertical speed directly with the hover throttles.

It has nothing to do with actual antigravity; it just makes it feel like antigravity to the pilot. Similar to the Flying Bedstead's gimbaled jet engine.

This business of an easier altitude ans vertical speed control has been solved by both the old Arrive MFD and computerex's AutoHover MFD. The former has that nice auto-throttle feature, while the latter allows you to use main engines for hovering with tail-sitters. A combination of both would be cool.

Ah, I see.

If I were to make a ship like we've been discussing (4 gimballed engines), I'd definitely include a custom autopilot for that sort of thing, which would throttle the engines appropriately and allow for "high level" control of vertical velocity combined with forward/back, and rotate/throttle the engines accordingly.

On that note, the descent velocity hold is nice for manually flying, but if you had a landing autopilot, wouldn't it be more efficient to wait longer before decelerating and have only a very short period of constant-velocity descent right before touchdown?

 

[Koriel]

.....wouldn't it be more efficient to wait longer before decelerating and have only a very short period of constant-velocity descent right before touchdown?

The short answer is yes and for short hops a ballistic style would be the most efficient.

The question is how close do your targets have to be before ballistic profile doesn't save fuel and how far before it is better to go into a orbit.

And exactly how much fuel are we really saving.

And perhaps the most interesting part is the more fuel we save the less room for error and the higher thrust will be on touch down.
These pads are rather close to the buildings.
Makes me wonder about flying debris.

 

[Andy44]

If I were to make a ship like we've been discussing (4 gimballed engines), I'd definitely include a custom autopilot for that sort of thing, which would throttle the engines appropriately and allow for "high level" control of vertical velocity combined with forward/back, and rotate/throttle the engines accordingly.

Cool.

On that note, the descent velocity hold is nice for manually flying, but if you had a landing autopilot, wouldn't it be more efficient to wait longer before decelerating and have only a very short period of constant-velocity descent right before touchdown?

Theoretically, yes, it would be best to calculate the exact engine burn time, at max thust, it would take to check your ballistic descent and come to a stop with your landing gear kissing the regolith.

But since your delta-V isn't instantaneous, you'll have to do a reverse gravity-turn along the way. You also want to build in time for the crew to deal with contingencies and make decisions. Apollo LM broke the gravity turn up into two phases, the braking phase, followed by the pitch-over and the final approach+hovering phase. This wasted some propellant, but the Moon's low gravity made it acceptable and it gave the crew a nice procedure with built-in abort options along the way, as well as a way to stear to new landing sites if the current one is obstructed.

If you wait until the last minute to burn at full thrust, any problems with your engine or your attitude control and you're having a very bad day, ending in a crash.