Author Topic: Are Commercial Crew Vehicles Usable/Upgradeable for Beyond-LEO Needs?  (Read 63073 times)

Offline jtrame

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Now doubt there is a lot that we still need to work out to implement a reusable transportation system.  NASA has been wanting to invest in some of technologies we'll need, and some is being done in private industry, but it certainly needs more work.

So in the near-term the cheaper solution will likely involve throwing away perfectly good hardware, and that is going to barrier to doing more in space because we are not able to lower the costs fast enough.

To change this is going to require a change in mindset, and the willingness of Congress to allow NASA to help perfect a number of needed technologies.  But based on the spending priorities Congress currently has I'm not sure when NASA will be able to help with this challenge, so that leaves it up to the private sector.

I think people would be surprised at how much lower the costs would be for some type of standard production "Mission Module".  Most of the expensive parts stay in the capsule and the "Mission Module could be fairly simplified.  What really gets costs cranking for NASA is that they have to do a one-off design and getting the mass into orbit.  If you had to design a new mission module from scratch every time you flew one then the costs would be fairly high.  However if you designed a standard module and then just kept building to that standard design your costs come down a lot.  You then place that with lower costs to orbit you get something that could dramatically lower prices.  Not enough to get into the 1/2 Million dollars to Mars cost that Musk wants but enough to be a good start until more re-usability is figured out.

If you base it on an already existing design (Cygnus) that is using a pressure vessel still in production (Thales Alenia Space) then you start to get that advantage.  The Thales Alenia modules are available in different lengths as well, so you could choose the amount of volume needed by the mission.

Offline jongoff

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I think what you are looking for is here:

Quote
Electrodynamic tethers (EDTs) are long conducting wires, such as one deployed from a tether satellite, which can operate on electromagnetic principles as generators, by converting their kinetic energy to electrical energy, or as motors, converting electrical energy to kinetic energy.[1] Electric potential is generated across a conductive tether by its motion through a planet's magnetic field.
http://en.wikipedia.org/wiki/Electrodynamic_tether

Yeah, I almost mentioned them, but didn't want to muddy the waters. ED's are useful, but you probably can't realistically use an ED tether to capture a spacecraft into LEO. Not enough thrust over the short amount of time you're low enough to get useful currents (which require plasma to close the circuit). They're great for propellantless reboost in LEO, and even some maneuvers around in LEO, but not something that scales well for capture (which I believe is what the original question was about--capturing spacecraft stacks back into LEO so you could use them again, and so the return vehicle only had to be LEO-rated).

~Jon
« Last Edit: 10/08/2014 06:22 PM by jongoff »

Offline JasonAW3

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Now doubt there is a lot that we still need to work out to implement a reusable transportation system.  NASA has been wanting to invest in some of technologies we'll need, and some is being done in private industry, but it certainly needs more work.

So in the near-term the cheaper solution will likely involve throwing away perfectly good hardware, and that is going to barrier to doing more in space because we are not able to lower the costs fast enough.

To change this is going to require a change in mindset, and the willingness of Congress to allow NASA to help perfect a number of needed technologies.  But based on the spending priorities Congress currently has I'm not sure when NASA will be able to help with this challenge, so that leaves it up to the private sector.

I think people would be surprised at how much lower the costs would be for some type of standard production "Mission Module".  Most of the expensive parts stay in the capsule and the "Mission Module could be fairly simplified.  What really gets costs cranking for NASA is that they have to do a one-off design and getting the mass into orbit.  If you had to design a new mission module from scratch every time you flew one then the costs would be fairly high.  However if you designed a standard module and then just kept building to that standard design your costs come down a lot.  You then place that with lower costs to orbit you get something that could dramatically lower prices.  Not enough to get into the 1/2 Million dollars to Mars cost that Musk wants but enough to be a good start until more re-usability is figured out.

If you base it on an already existing design (Cygnus) that is using a pressure vessel still in production (Thales Alenia Space) then you start to get that advantage.  The Thales Alenia modules are available in different lengths as well, so you could choose the amount of volume needed by the mission.

Essentially you'd assemble them kind of like a space going Winnabego RV.  Start with a basic can and internal layout.  Pre run the wiring harnes and assemble internal components and plumbing as needed.

  Orbital itself has suggested a number of different exterior designs including both short and stretch can designs with both docking ports on the ends and in the middle, and even a design with a cupola similar to the one on the ISS already.
They've even done art with one of their cans using an Inflatable Hypersonic Decelerator heat shield as a life boat.

At least they're thinking ahead.  If the Russians DO splash the ISS, with Orbital's modules, we could have a new oner ihn place in a couple of years.
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Offline Brovane

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Dracos, of course. Remember, Orion had thrusters as backup to its OMS engine, and that was for lunar orbit. Certainly not Superdracos. Remember, Dragon launches with all that abort propellant which it could use (if it doesn't have enough prop for full vertical landing back on Earth, it may still have enough for parachute assist), and one could imagine a slight increase in propellant. You'd need about 500m/s or so, depending on just how fast of a transit you want. If you can afford to wait, you need a lot less propellant.

You want to use a 400N Draco engine to move between EML-1/EML-2 and LEO? 
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Online mmeijeri

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You want to use a 400N Draco engine to move between EML-1/EML-2 and LEO?

Not between LEO and L1/L2, but from L1/L2 back to Earth.
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Offline Brovane

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Not between LEO and L1/L2, but from L1/L2 back to Earth.

Ok the question still applies going from EML1/2 back to Earth.   You are going to need to apply some Delta-V to the vehicle.   
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Ok the question still applies going from EML1/2 back to Earth.   You are going to need to apply some Delta-V to the vehicle.   

Only a couple of hundred m/s. That's part of why returning straight to Earth is so much easier than returning to LEO.
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Offline Brovane

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Only a couple of hundred m/s. That's part of why returning straight to Earth is so much easier than returning to LEO.

I guess it is doable.  However some consideration will have to given to modifying the current Draco thrusters to support vastly increased propellant tanks.  You are probably looking at 1000-1500 kg of propellant.  However this is all dependant on the wet mass of the DragonV2.

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It's very similar to what your typical apogee thruster is expected to do.
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Offline Robotbeat

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The low thrust of Draco isn't a concern for capturing at EML1/2.
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Offline Lars-J

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The low thrust of Draco isn't a concern for capturing at EML1/2.

Indeed. If it has enough kick to deorbit from LEO in a reasonable time, then it sure as heck won't be a problem to use regular Draco thrusters to enter and leave EML1/2.

The only concern will be the amount of propellant, but for that purpose it should have enough. (assuming a FH launches it on a EML1/2 transfer trajectory)

People seem to have this concern that thrust is needed once you get beyond LEO. But unless you are propulsively being captured in (or departing from) low orbit around a planetary body or major moon, that simply isn't the case. Efficiency will beat out thrust.
« Last Edit: 10/09/2014 06:55 AM by Lars-J »

Offline MP99

The low thrust of Draco isn't a concern for capturing at EML1/2.

Indeed. If it has enough kick to deorbit from LEO in a reasonable time, then it sure as heck won't be a problem to use regular Draco thrusters to enter and leave EML1/2.

The only concern will be the amount of propellant, but for that purpose it should have enough. (assuming a FH launches it on a EML1/2 transfer trajectory)

People seem to have this concern that thrust is needed once you get beyond LEO. But unless you are propulsively being captured in (or departing from) low orbit around a planetary body or major moon, that simply isn't the case. Efficiency will beat out thrust.
I'm told that when two large ships need to rendezvous at sea, then a single man tugging on a rope is sufficient to draw them together.

Similarly, in space, as long as there is no time pressure (usually due to being deep in a gravity well), then the amount of thrust doesn't really matter, within reason. If your thruster has 1/100th the thrust, then just operate it 100x as long, and you'll end up with the same total impulse. It's only when you get to ridiculously low thrust (EG SEP), that the acceleration time becomes a major issue.

Cheers, Martin

Offline Lars-J

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Only a couple of hundred m/s. That's part of why returning straight to Earth is so much easier than returning to LEO.

I guess it is doable.  However some consideration will have to given to modifying the current Draco thrusters to support vastly increased propellant tanks.  You are probably looking at 1000-1500 kg of propellant.  However this is all dependant on the wet mass of the DragonV2.

How is does a couple of hundred m/s imply the need for a "vastly increased propellant tanks"?

What kind of mission profile are you imagining?

Offline WindyCity

Forgive me if this has been already discussed.

Could a BA330 be mated with a Dragon 2 for BEO missions? I don't know what additional ECLSS would have to be added, but from what I've read, the radiation and meteorite shielding of the hab would appear to be adequate for travel in deep space. Also, the BA330 has a propulsion system. Could the hab be stationed in LEO and then hooked up to the crew capsule and then boosted onto an interplanetary trajectory?

Offline AncientU

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Forgive me if this has been already discussed.

Could a BA330 be mated with a Dragon 2 for BEO missions? I don't know what additional ECLSS would have to be added, but from what I've read, the radiation and meteorite shielding of the hab would appear to be adequate for travel in deep space. Also, the BA330 has a propulsion system. Could the hab be stationed in LEO and then hooked up to the crew capsule and then boosted onto an interplanetary trajectory?

That is basically what the BA-330 is designed for... and the propulsion system is a 'tug' that moves the entire bit beyond LEO... or beyond whatever location (EML-1/2 for instance).  I've not actually heard mention or seen written text that showed docked vehicle like Dragon 2 being accelerated with the BA-330, so the stresses at docking mechanism may be be limiting.

Great Article on the topic:
http://www.nasaspaceflight.com/2014/02/affordable-habitats-more-buck-rogers-less-money-bigelow/

Quote
Family of Tugs:

The documentation also portrays a family of tugs that could be used in conjunction with Bigelow habitats for use beyond Low Earth Orbit.

The fleet consists of the Standard Transit Tug, the Solar Generator Tug, the Docking Node Transporter and the Spacecraft Capture Tug.

These tugs could be used to push the various Bigelow Habitats – and other payloads – to specific destinations in LEO, L2, Cislunar space and beyond.

The four tugs are designed to be grouped together in various combinations, depending on the mission requirements. Notably, they are sized for launch on SpaceX’s Falcon Heavy rocket.

The tugs could be launched independently, prior to rendezvous with other elements in LEO to form a complete transport system. Each of these tugs share propulsion, docking and avionic systems.

Quote
The BA 330-DS:

The documentation also offers NASA a deep space version of its habitat, the BA 330-DS, for use beyond Low Earth Orbit. The BA 330-DS could be used by NASA, for example, at a Lagrange point or in lunar orbit.

The BA 330-DS would be very similar to its LEO version. The main difference would be related to radiation shielding.
« Last Edit: 10/10/2014 06:44 PM by AncientU »
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Offline docmordrid

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The enhanced shielding is likely the water bags that have been talked about since forever. I've been wondering of they also contain soluble boron compounds for neutrons, if the water "bags" are boron-silicone, or both?

Anyhow, the core looks strong enough to handle axial loads from thrust,
« Last Edit: 10/11/2014 01:57 AM by docmordrid »
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Offline AncientU

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There you go.
Room for twelve crew, six per BA-330.
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Online mmeijeri

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How is does a couple of hundred m/s imply the need for a "vastly increased propellant tanks"?

Roughly 700 m/s @ 320s Isp should require about 25% of the Dragon's dry mass in propellant.
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Offline Robotbeat

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How is does a couple of hundred m/s imply the need for a "vastly increased propellant tanks"?

Roughly 700 m/s @ 320s Isp should require about 25% of the Dragon's dry mass in propellant.
Soyuz's 390m/s delta-v (195m/s each way) would be sufficient if you use 16-day traverses.
« Last Edit: 10/11/2014 06:05 PM by Robotbeat »
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In that case you'd need roughly 13% of the dry mass in propellant. And additional consumables of course.
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