Ares or DIRECT?

[Spicer]

Direct is a wonderful option, but it's too late in the game. The shuttle will be shut down within a year or so...hopefully a bit longer. The DragonX capsule will probably take over for ferry trips to the ISS, and eventually the Ares I will take over servicing the ISS.

In reality the best option for Orion, is on top of a Delta IV, until the Ares is totally shaken out. Who knows what will really happen.

 

[tblaxland]

In reality the best option for Orion, is on top of a Delta IV, until the Ares is totally shaken out.

Pun intended?

 

[Talon1]

Yeah, I think DIRECT launchers are best.

 

[simcosmos]

Although currently being a bit in 'away mode' decided to drop-by in this particular post for a very quick comment.

Will not vote in the poll but, if had voted, my choice would perhaps be dependent of additional context being provided to the question being asked, I mean:

a) Would vote in DIRECT for NASA's exploration path (plus some EELV synergies and a few extra assumptions regarding exploration architecture options) IF the context is based on multiple constraints (technical, budget, time frame, experience base, political, sustainability, crewed + robotic missions equilibrium, etc, etc)

b) However, IF the context of the poll's question would be free from all or, at least, free of some of such multiple constraints, I would probably not vote in DIRECT (or, in generic terms, would not vote in a Shuttle Derived Launch Vehicle) and would instead vote in a clean sheet launcher (in a sense, ARES is currently more and more close to a clean sheet concept than being SDLV by the way), but – and this is kind of important – I think that if going to the clean sheet route (and again, IF free of some current constraints) the best would probably be to do it in a ‘better way’ (in lack of better words) and, from this *specific context*, would prefer that such clean sheet conceptual vehicle could bring back to the trade space a kerolox design for boosters and/or core (or even to both components).

António

Note1: In an alternative reality, something like DIRECT launchers could later be 'transformed' (at a given cost and under a very long-term operational time + other additional assumptions) to allow some kind of such kerolox configuration change to its components but again, this is only a very conceptual and personal side thought, nothing else beyond that!)

[FONT=&quot]Note2 / disclaimer: only to be extra clear, all the above is just and only my personal opinion and has no relation to what several other DIRECT Team members might or not think about the topic
[/FONT]

 

[RocketMan_Len]

Additionally, the wings are also the parts with the worst ratio of reentry energy and mass. You don't want to store stuff inside your wings, which boils easily.

Well... if you're concerned about re-entry, the tanks will be empty *anyway*.


-----Post Added-----

Putting fuel in the wings comes with it own weight penalties. A wing tank has a much higher surface area to volume ratio than a spherical or cylindrical tank. Also, additional reinforcing is required because the tank shape is not as efficient at distributing the structural loads of the pressure in the tank. These two factors increase the dry mass/wet mass ratio and thereby reduce your payload fraction.

True enough. But as I said earlier, these are the type of design trade-offs that have to be done... no matter what type of system you use.

 

[movieman]

For a DC-X sized vehicle or larger, though, you can't carry both. Parachutes and rigging mass alot more than you might think, and if your engine fails to start on landing you're probably too low for back-up chutes to save you, anyway. If your crew is small, ejection seats might be a viable option for bail-out at low altitude.

For a DC-X style vehicle, you're landing with almost empty tanks, which gives you a huge crumple-zone below the crew if they're near the top. Certainly wouldn't be a good day, but they could probably walk to the hospital if some thought was given in the design to ensuring they could survive such a crash.

In addition, you'd probably have multiple engines and use far more of them to launch than to land; if you have eight engines, need two to land and four fail, then you still have 2x the required redundancy (OK, you're probably in trouble if all four are on the same side).

Whereas both of the winged spacecraft we've lost so far have killed the crews due to their wings falling off. Not a lot you can do when that happens, and it's a very likely scenario when you're pushing something with wings through high-velocity air with very high dynamic pressures.

 

[RocketMan_Len]

Whereas both of the winged spacecraft we've lost so far have killed the crews due to their wings falling off. Not a lot you can do when that happens, and it's a very likely scenario when you're pushing something with wings through high-velocity air with very high dynamic pressures.

Not *entirely* accurate. Challenger was lost because an O-ring burn-through ignited the main fuel tank... the explosion destroyed the orbiter, not a wing falling off.

As for Columbia - if you punch a large hole in the wing, even at low velocities that's a bad thing to happen. Of course - if you punch a large hole *anywhere* on your vehicle, Bad Things Will Happen.

 

[zerofay32]

Challenger wasn't an "explosion." The heat from the O-ring burnt through the lower SRB attachment causing it to fail. Once the lower connection was lost the SRB shifted outward causing the vehicle to yaw far enough that it began to break apart from aerodynamic stress. The cloud the enveloped the vehicle was first the LOX and Hyd instantly turning to gas after the ET began to break apart. After that the propellant in the air then combusted from contact with the SRB exhaust. So the explosion of the propellants happened after vehicle break up as so was not the principal cause of the incident. Of course I'm just splitting hairs .

Zerofay32

 

[RocketMan_Len]

Challenger wasn't an "explosion." The heat from the O-ring burnt through the lower SRB attachment causing it to fail. Once the lower connection was lost the SRB shifted outward causing the vehicle to yaw far enough that it began to break apart from aerodynamic stress. The cloud the enveloped the vehicle was first the LOX and Hyd instantly turning to gas after the ET began to break apart. After that the propellant in the air then combusted from contact with the SRB exhaust. So the explosion of the propellants happened after vehicle break up as so was not the principal cause of the incident. Of course I'm just splitting hairs .

I know - technically, it wasn't an 'explosion' any more than a boiler rupture is an 'explosion'. To the average spectator, though, it would certainly be considered an explosion.

 

[Urwumpe]

I know - technically, it wasn't an 'explosion' any more than a boiler rupture is an 'explosion'. To the average spectator, though, it would certainly be considered an explosion.

Except the lack of a good explosion sound. It was almost some sort of anti-explosion audio-wise. It became a bit louder and then very very silent.

A boiler rupture, BTW, is technically an explosion. You have a enclosed vessel which bursts under overpressure.

But Challenger did not burst under overpressure, it was torn apart by aerodynamic forces.

 

[movieman]

But Challenger did not burst under overpressure, it was torn apart by aerodynamic forces.

As was Columbia, which was rather my point. A capsule or DC-X style cone can generally take much higher stresses than a winged vehicle and live to tell about it... even with a hole in the side, if your engines or parachutes still work you can still land; particularly as you don't have to get to a runway in order to land.

Several people have survived flying backwards in a Soyuz during re-entry, but no-one has ever survived that in a winged spacecraft.

 

[Urwumpe]

As was Columbia, which was rather my point. A capsule or DC-X style cone can generally take much higher stresses than a winged vehicle and live to tell about it... even with a hole in the side, if your engines or parachutes still work you can still land; particularly as you don't have to get to a runway in order to land.

Yes, but you have different failure paths. the DC-X would not be more robust automatically. If you would have a heatshield damage on the DC-X, which is not impossible, the plasma could cut through the DC-X structure just as good as through the space shuttle wing. Maybe even better. The wing held the plasma longer than expected, because the dense structure dispersed the plasma stream for a while.

Several people have survived flying backwards in a Soyuz during re-entry, but no-one has ever survived that in a winged spacecraft.

Nobody also nearly drowned and froze to death at the same time in a winged spacecraft.

 

[cjp]

(About storing fuels inside the wings):

Well... if you're concerned about re-entry, the tanks will be empty *anyway*.

Except, when you reverse the sequence, e.g. when you land an expedition on mars, and don't do ISRU, then you'd have your take-off fuel on board when you do the re-entry (which, technically, is an entry, not a re-entry).

But maybe nobody was seriously proposing using winged mars landers.

Talking about ISRU... these plans (at least DIRECT) talk about creating methane (and oxygen?) on Mars, right? How efficient is that as a rocket fuel? Can rocket engines be made that accept multiple fuels (like LPG car engines), to give you a better performance when using the better fuel? I'm thinking about the concept of having a spacecraft that can operate on both Earth and Mars, and the ISRU option gives interesting design limitations.

I've once read another concept, that used 2 CO + O2 as rocket fuel. I'm not a chemical engineer, but it doesn't sound very efficient to me. But maybe it's good enough for a Mars SSTO.

 

[Eagle]

Talking about ISRU... these plans (at least DIRECT) talk about creating methane (and oxygen?) on Mars, right? How efficient is that as a rocket fuel? Can rocket engines be made that accept multiple fuels (like LPG car engines), to give you a better performance when using the better fuel? I'm thinking about the concept of having a spacecraft that can operate on both Earth and Mars, and the ISRU option gives interesting design limitations.

I've once read another concept, that used 2 CO + O2 as rocket fuel. I'm not a chemical engineer, but it doesn't sound very efficient to me. But maybe it's good enough for a Mars SSTO.

Methane/LOX gives good ISP around 380s. Better than RP-1. The difficulty is storing it because of its high vapor pressure and low boiling point. Its somewhat easier on a colder Mars though.

Generating Methane or other rocket fuels on Mars is endothermic (takes energy to do it) because the reaction to burn the fuel must be exothermic. Its no more efficient then generating Hydrogen and Oxygen from water using electrolysis.

But maybe the efficiency question is it cheaper/easier/safer/more scientific to truck a full return stage all the way from Earth or launch the return stage early and empty and fuel it slowly for 6 months?

 

[Zatnikitelman]

Throw a RTG with methane production facility and inflatable tank to Mars on a Delta II, then when the next window opens, send crew with enough fuel to get there, but not back. Plug the ascent stage up to the inflatable tank, launch to orbit, fuel up the return stage (maybe the same) light the engine and come home. If you're using the Sabatier process then you also get water out of the deal and that's less water that you have to carry to Mars.
Sounds straight forward to me.


-----Post Added-----


Or we could just filter it out of the atmosphere...
http://www.cnn.com/2009/TECH/space/01/15/mars.methane/index.html

 

[RocketMan_Len]

As was Columbia, which was rather my point. A capsule or DC-X style cone can generally take much higher stresses than a winged vehicle and live to tell about it... even with a hole in the side, if your engines or parachutes still work you can still land; particularly as you don't have to get to a runway in order to land.

You don't *have* to get to a runway in order to land a winged vehicle, either... as long as you don't expect it to take off ever again.

Several people have survived flying backwards in a Soyuz during re-entry, but no-one has ever survived that in a winged spacecraft.

Backwards...? With the heat-shield facing the wrong way...? I've never heard of that happening - can you provide a reference?


-----Post Added-----

(About storing fuels inside the wings):

Except, when you reverse the sequence, e.g. when you land an expedition on mars, and don't do ISRU, then you'd have your take-off fuel on board when you do the re-entry (which, technically, is an entry, not a re-entry).

I've never been referring to a Mars vehicle - just Earth-orbit-and-back. Mars presents a different set of problems, which I'm not even attempting to work out.


-----Post Added-----

A boiler rupture, BTW, is technically an explosion. You have a enclosed vessel which bursts under overpressure. .

Nope - an explosion is defined by the velocity the shock-wave propagates at. I don't recall what the exact figure is... somewhere in the twenty-meter-per-second range... but a boiler-rupture falls below that threshold.

(Which is one of the reasons rocketry people are having such trouble in the US - the authorities are claiming that rocket motors 'function by explosion' when *by their own definition* the reaction is far slower than what is considered to be an explosion... )

 

[Orbinaut Pete]

More funding for NASA, DIRECT being considered as a "fair game" as an alternative to Ares"

http://www.nasaspaceflight.com/2009/02/extra-nasa-funds-initial-step-towards-gap-reduction/

 

[Zatnikitelman]

They listed SpaceX there too!

 

[movieman]

You don't *have* to get to a runway in order to land a winged vehicle, either... as long as you don't expect it to take off ever again.

Crash-landing in the shuttle is generally regarded as non-survivable; it would snap behind the crew cabin and the crew would almost certainly be killed as it tumbled along the ground. You simply cannot make the structure of a winged spacecraft as solid as that of an aircraft with current propulsion technology, and as a glider you're going to land much faster than a crashing airliner.

Backwards...? With the heat-shield facing the wrong way...? I've never heard of that happening - can you provide a reference?

At least two Soyuz have re-entered backwards due to the service module failing to separate from the descent capsule; as soon as the service module broke up, aerodynamic forces reoriented them to the correct angle for reentry. I very much doubt that any realistic near-term winged spacecraft could survive the same, though they're less likely to get into that situation if they're a single stage.

Here's one:

http://en.wikipedia.org/wiki/Soyuz_5

 

[Urwumpe]

Still, please remember that Soyuz 5 was more luck then anything. The hatch was just seconds away from failure when the craft finally reoriented.