Deep Space and Interplanetary Exploration - The Universe is Timeless

[Wrangler]

What does you guys think about US Congress ordering & funding Nasa's Habitat intended for the Orion's trip to say the moon?  I had always thought the they would actually need build something bit more reusable like interplanetary ship with Orion docking with it verse a attached Camper.

[kato]

The problem with reusable interplanetary ships - even just for the Moon - is the rather high delta-v requirement. After all you need to park it in Earth Orbit again to reuse it. For low earth orbit to low lunar orbit and back to low earth orbit we're talking 7.8 km/s here, enough that at least 70% of that ship will be just fuel (for comparison, at about 6 km/s delta-v we're talking one ton fuel per ton dry mass, and it doesn't scale geometrically).
Orion is based on the standard way of returning to Earth: by not stopping and dropping straight into the atmosphere to lose speed. As such, the DSH will always only make a one-way trip.

[Wrangler]

The problem with reusable interplanetary ships - even just for the Moon - is the rather high delta-v requirement. After all you need to park it in Earth Orbit again to reuse it. For low earth orbit to low lunar orbit and back to low earth orbit we're talking 7.8 km/s here, enough that at least 70% of that ship will be just fuel (for comparison, at about 6 km/s delta-v we're talking one ton fuel per ton dry mass, and it doesn't scale geometrically).
Orion is based on the standard way of returning to Earth: by not stopping and dropping straight into the atmosphere to lose speed. As such, the DSH will always only make a one-way trip.

Even if they went with Plasma Engine aka the Variable Specific Impulse Magnetoplasma Rocket, it won't be possible.  I know nuclear propulsion is a long shot to have established, but the ship's fuel won't be as strained it?

I guess I'm a dreamer i guess.  :)

[kato]

Both VASIMR and other NEP also need propellant. And for the same thrust they need the same amount of propellant as any other engines. Newton's 3rd law in (re)action.

Pretty much the only way to get around without propellant is solar sailing.

[BirdofPrey]

At least for LEO insertion, there is the possibility to use aerobraking, though I imagine that might cause some controversy initially.

[rebs]

Just felt like depositing another pic of Pluto's icy plains...

Here it looks like pock marks on a whitened fruit rind, outlined and highlighted by graceful looking fractures and faults frozen over.



(Looks like a frozen Brontosaurus slightly up from center (Sing it... "You say Apatosaurs, I say Brontosaurs..."  ;) )

[rebs]

Pretty much the only way to get around without propellant is solar sailing.

Luckily, this is a goal that is in sight and reach.

The main problem I see would be trying to "tack" against the Sun to come back to Earth from Mars or or further out.  Propellant would still be needed due to the not-quite-predictable nature of solar wind energy.

But that's me imagining.  There might be a wonderful solution for this out there that I haven't read about yet.

I hope :-)

[kato]

Ikaros uses a quite ingenious way to adjust the pressure on its sail in such a way that it can shift the sail into an angle towards the wind (more precisely: towards the photon source - Ikaros sails on photons, not the lower-pressure solar wind). That should also allow tacking, at least it seems to have worked on the way inwards to Venus:



The adjustment works with LEDs embedded into the edges of the sail. These can be set to either reflect or refract incoming photons, thus providing different thrust. If you set them differently on opposite edges of the sail, the sail will thus turn. It's more complicated than it sounds, since to keep the sail unfurled Ikaros is also spinning at 20 rpm.
Ikaros also kept thrusters in reserve in case it'd need to turn the sail promptly. Basically like a back-up diesel on a sailship...

[Daryk]

Interesting... is it using the sail to shed orbital velocity and letting gravity pull it in?

[kato]

Shedding orbital velocity would push it outwards away from the sun. What it basically did was do that relative to the ballistic path that the initial launch (as a passenger with Akatsuki) had put it on, thus altering her path distinctly. However it didn't just do that.

That B-plane diagram above on the right (with the "projected points") shows where Ikaros would fly by Venus if it stopped adjusting its path on a certain day. If you don't steer the sail then the pressure on the sail would mean that this flyby point would constantly move "outwards" relative to Venus, on the above diagram that means it'd move from left to right.

For the first six weeks they angled and steered the sail in such a way that the projected flyby point instead went "inwards" - i.e. they sailed angled against the wind, until they reached a point where Ikaros' path wouldn't take her by Venus "behind" her but instead "in front" of her relative to the sun. End of september they then dropped this steering and as expected the wind pushed the craft "outwards".

Edit: This might explain it better in 2D, as a quick-and-dirty MS Paint picture:



The black line is your path that you were pushed on. Since you have a sail, the solar wind (here coming from the left) pushes you progressively further off, following the red line. What Ikaros did was turn into the wind in such a way that they followed the green line.

[Daryk]

Man, that tells you how long it's been since I actually had to do any orbital mechanics.  :-[

Thanks for the clarification!

[kato]

See above edit for further clarification  ;)

[Daryk]

It does help, thanks again!

[rebs]

I'm glad I spoke up!  ;D

[Sabelkatten]

Both VASIMR and other NEP also need propellant. And for the same thrust they need the same amount of propellant as any other engines. Newton's 3rd law in (re)action.

Pretty much the only way to get around without propellant is solar sailing.

You're forgetting exhaust velocity (I_sp). Double exhaust velocity and you get twice the delta-v for the same amount of reaction mass. Since the electric/plasma drives can get several times the velocity of chemical drives you can get a lot better delta-v (assuming, of course, you can stand the less-than-impressive acceleration... ;) ).

[kato]

That's why I said "for the same thrust". Because that's the problem with ion thrusters, their thrust is measured with a milli in front instead of a kilo...

[Lazarus Jaguar]

Maybe we should just stop putzing around slowboating it and dust off Orion?

[BirdofPrey]

Because the orion is insane.
It won't get you into orbit, but nuclear thermal rockets are good for once you're in space.

[ANS Kamas P81]

Because the orion is insane.
It won't get you into orbit, but nuclear thermal rockets are good for once you're in space.

No, the One True Orion is idiotically powerful and efficient.  Frankly using any engine of that level of energy is going to be a case of the Kzinti Lesson, even with the shaped-charge system they'd come up with.  Pretty clever, I thought, and the idea of thermonuclear shaped-charges really made "nukes in space" effective.

[Sabelkatten]

That's why I said "for the same thrust". Because that's the problem with ion thrusters, their thrust is measured with a milli in front instead of a kilo...

Thrust also scale with exhaust velocity.

The basic problem with (almost) all high-I_sp drives is that high exhaust velocity = high energy levels = high engine temperature. Ion engines also have a problem with electrical charges and of course whatever power plant you use might get impractically heavy, but at the core is that simple fact that if you try to handle too much hot plasma your engine might melt... :P

Orion get around this by essentially blowing up its engine. The thrust plate only has to handle the plasma after it has dispersed and cooled down, and only for a short time with each firing.

[Maingunnery]

To imagine the things humanity could do if we ever get something as good as BT station-keeping drives.

[Daryk]

Even station keeping drives are pushing the limit of matter-anti-matter conversion.  Regular drives are well beyond it.

[marauder648]

Do we have any updates on Juno? That's due to arrive at Jupiter this year isn't it?  Should be a fascinating mission, they are going to see if Jupiter's got a core and see if they can detect liquid water under the ice of Europa and I think Gannimede.

[kato]

Juno will arrive on July 4th. Won't really study the moons, pretty focused on Jupiter itself - and her instruments are laid out for only that anyway.

[Natasha Kerensky]

What does you guys think about US Congress ordering & funding Nasa's Habitat intended for the Orion's trip to say the moon?

Not much.  Orion ostensibly still exists to take astronauts to and back from Mars, a ~2 year mission.  But Orion is a leftover jobs program from the defunct Constellation program to return astronauts to the Moon, and, among other problems, Orion doesn't have the internal volume, life support, or mission longevity to conduct more than ~30-day missions.  So NASA and taxpayers are spending billions of dollars for the wrong vehicle for the Mars mission, and now Congress has started spending billions more NASA and taxpayer dollars to put a Band-Aid on this problem.  Orion should have been terminated years ago, and NASA allowed to rationalize its post-Constellation human space exploration architecture without hanging the albatross of Orion's (and its launcher SLS's) huge budget and technical shortcomings around NASA's neck to preserve certain jobs in certain congressional states/districts.

The whole thing will likely come under White House review after the next election.  Whether the next White House cares enough after that review to fight the necessary political battles with Congress to reform and preserve NASA's human space exploration program remains to be seen.

I had always thought the they would actually need build something bit more reusable like interplanetary ship with Orion docking with it verse a attached Camper.

This really has nothing to do with reusability.  It's a question of allocating functions and capability.  The best approach is put in-space transport functions on a different vehicle from the vehicle that performs launch and entry/descent/landing functions.  The latter is usually the most dangerous phase of a mission, so you really want to simplify and make small the vehicle that carries astronauts up/down from the vehicle that carries astronauts from one planet's orbit to another planet's orbit.  Trying to do most or all of that on one vehicle creates a large, complex vehicle that is hard to make safe during launch accidents and is hard to keep safe during reentry.  Piling too many requirements and too much complexity on an EDL vehicle is one of the many lessons we learned on Shuttle (Columbia accident), but we're ignoring it on Orion, and as a result, the probabilistic risk assessments for Orion/SLS are actually coming in slightly worse than Shuttle.

[Lazarus Jaguar]

Just a thought, but if I hit tomorrow's Powerball jackpot, would I have enough to fund construction of my own Orion powered spacecraft?

[Sharpnel]

$1.4 Billion would barely be a drop in the bucket

[ANS Kamas P81]

On the topic of Jupiter...
http://www.gizmodo.com.au/2016/01/physicists-appear-to-be-closing-in-on-an-elusive-state-of-metallic-hydrogen/
Nature publication on the potential for solid metallic hydrogen.  Granted, they get a little speculative wonder-material-of-the-future with it at the end, but it's still a neat discovery waiting to happen.  With things like the laser compression at NIF and the kinds of pressure they're getting there, I wonder if there'd be a way to adapt the technology to lock down the research better?

Just a thought, but if I hit tomorrow's Powerball jackpot, would I have enough to fund construction of my own Orion powered spacecraft?

You could build a small one, but you damn sure won't get any fuel for it.  You'd basically end up with the world's most earthquake-proof house.

That said, can I come over and play Battletech there with you?

[kato]

Might be interesting regarding the solar sail discussion earlier:

After Hayabusa-1 suffered two out of three reaction wheels broken during touchdown operations, JAXA developed a "solar sail mode" to bring her back to Earth. Basically, the probe balanced between the single working reaction wheel (Z-axis) and photon pressure on its solar panels; it's also called "one wheel control".
For Hayabusa-2, currently enroute to Ryugu, JAXA further developed this balancing act into a regular flight mode; while Hayabusa-2 has four reaction wheels (X-, Y-, and two Z-axis) only one is used during the cruise phases. The spacecraft basically preserves a full XYZ set of reaction wheels for detail operations only - and the mode also saves fuel for the thrusters.

If anyone wants to look at the math: http://issfd.org/2015/files/downloads/papers/129_Mimasu.pdf

Hayabusa-2 just entered this flight mode again (after its December Earth flyby).

From a local aspect here a very bad development. Our only real space company here in my area builds up to a hundred reaction wheel sets per year in a local factory. As in they kinda have a commercial monopoly on that, globally.  ;D

[Sabelkatten]

I don't think they have to worry all that much... It's not like they've stopped mounting reaction wheels. :)

Still, an interesting side effect of that is that very large solar panels suddenly gets much more attractive. If you can make fine adjustments without using any fuel - even if the saved amount is very small - it can pay for quite a bit of extra panels.