Quote from: Robotbeat on 10/05/2014 03:04 pmI will say one thing: since both designs chosen were capsules, they are both relevant for any future BLEO missions and should be considered for inclusion by mission planners.None of these vehicles will be evolved for BLEO - they are too small. Be glad to talk on another thread about it if you want...
I will say one thing: since both designs chosen were capsules, they are both relevant for any future BLEO missions and should be considered for inclusion by mission planners.
Yes. But there is limited use in taking them with you past some kind of L1/2 gateway station.
Aerobraking takes too much time with a crew aboard.
It believe it's passing through the radiation belts too many times that TomH may have been thinking about.
My point was that Dragon and CST-100 and Orion and Apollo command module, etc, all would need an extra module, so all are big enough with a module and none are big enough without a module, assuming beyond short trips to and from an EML gateway or something. And they are big enough for a few days.I mean Gemini was cartoonish lot small for 2 guys (WAY smaller than CST-100, Dragon, etc), and they spent 2 weeks in it. Dragon or CST-100 are like mansions compared to Gemini.
If the habitat is launched/built separately and put in a permanent cycling orbit, then the capsule could rendevous with it during Earth approach, go along with it on the mission, then separate and return to Earth on the return leg.
...and you have astronauts watching the Earth go by over and over while they cannot land, likely enduring psychological stress from being so near physically, while still so far away temporally.
Orion is perfectly suited for.....absolutely no mission
But having BEO rated avionics, heat transfer through heat plates, high distance comm system, long term ECLSS, BEO astrogation capabilities, limited radiation protection for crew, etc. those thing are the hard part.
Quote from: TomH on 10/06/2014 03:54 amOrion is perfectly suited for.....absolutely no missionTo the contrary I think Orion is the right size to taxi a crew of four between Earth and a space station in the lunar vicinity, e.g EML1, EML2, or DRO. The current design is too heavy for this (due to the parachute issue), and no one who knows why seems willing to say. I've expressed my guess that it's the result of structural mass left over from CxP mission requirements that is not required in this taxi role. That mass could be taken out by redesigning the structure. Alternately, EFT-1 may show a way to reduce mass, if it indicates the heat shield is over-built.
In my opinion (for what it's worth) Orion should have been largely composite in structure, much like the ATK Liberty proposal which I also think might have been a 'mere' 4.5 meters in diameter and doubtlessly thousands of kilos lighter than Orion's large aluminium/lithium etc structures.
Quote from: MATTBLAK on 10/06/2014 10:54 amIn my opinion (for what it's worth) Orion should have been largely composite in structure, much like the ATK Liberty proposal which I also think might have been a 'mere' 4.5 meters in diameter and doubtlessly thousands of kilos lighter than Orion's large aluminium/lithium etc structures. They did build a composite version of Orion, to see what the issues were. It wasn't any lighter. Ironically, that composite version of Orion then BECAME Liberty. :-) Cheers, Martin
So are people thinking that Commercial Crew capsule vehicles (i.e. CST-100 and Dragon V2) could be an interim solution for short duration exploration? For non-NASA missions, or if for some reason the Orion is not available?Or that they could be used more expansively than that?
Quote from: QuantumG on 10/06/2014 02:07 amIt believe it's passing through the radiation belts too many times that TomH may have been thinking about.That's true also, however a habitat returning from Mars would need dozens of passes through the very upper atmosphere on a very high apogee ellipse. It would have no TPS at all and could incur very little -ΔV on each pass. I am no expert in orbital mechanics, however I believe it would take much more than the 2 weeks max you believe it would. That means more mass for food, O2, etc., and you have astronauts watching the Earth go by over and over while they cannot land, likely enduring psychological stress from being so near physically, while still so far away temporally.
IMHO, NASA should be building landers, either for Moon, Mars, or both (preferably Moon) which could double as craft to visit asteroids or Phobos/Deimos. Maybe also a deep space gateway in cislunar space or near Mars, perhaps also Mars habitats and infrastructure, maybe a SEP-based transit vehicle. Launch vehicles and now capsules are totally doable by commercial entities. It's a much better use of restores for NASA to be building landers and such, just buying the services for launch or even now crew taxis and logistics from the likes of Boeing, SpaceX, ULA, Orbital/ATK, Sierra Nevada, and Blue Origin.
That does reduce deep space mission mass. It also means, however, that upon return to Earth, the hab must be decelerated to orbital V prior to rendezvous with a taxi, which means taking the prop with you to deep space and back, or you rendezvous with a tanker prior to Earth arrival. The other choice is a taxi must rendezvous with the hab as it approaches Earth, and you lose the hab.
2. LEO to the region of the Moon and back - this would be a reusable vehicle, likely refueling and refurbishing in LEO. Getting to the Moon is pretty straight forward, but returning to LEO requires perfecting new techniques. But if we can't figure this part out then we're not going to be able to afford to send many people BEO.
If you think Commercial Crew vehicles will be adaptable for BEO applications, please state what those applications are.
It says Dragon v2 dry is about 4,200 kg.
Quote from: ngilmore on 10/06/2014 04:24 pmIt says Dragon v2 dry is about 4,200 kg. I'm pretty sure that's just an unsourced copy-paste from the Dragon v1 mass - it should be significantly higher than that with Superdracos/extra tanks, ECLSS, windows &c. Probably more like 6+ tons dry.
Need to add LAS mass
Quote from: AncientU on 10/06/2014 04:38 pmNeed to add LAS massYes, thank you, even more margin. NASA says the gross liftoff weight of the LAS is 7,314 kg.http://www.nasa.gov/pdf/617408main_fs_2011-12-058-jsc_orion_quickfacts.pdfThe same NASA fact sheet says the total Orion system gross liftoff weight is 31,380 kg.So that should be top line comparison when asking if commercial crew vehicles could be adapted for BEO.
2. LEO to the region of the Moon and back - this would be a reusable vehicle, likely refueling and refurbishing in LEO. Getting to the Moon is pretty straight forward, but returning to LEO requires perfecting new techniques. But if we can't figure this part out then we're not going to be able to afford to send many people BEO.Anyways, that's part of the reason why I don't think today's Commercial Crew capsules are part of the evolutionary line of vehicles that we'll need in the future - I just don't see how they help us scale up the number of people leaving LEO. And isn't that really the goal?
In terms of going to and from the region of the moon direct reentry to earth would probably be the best bet. It costs less in delta V and you get your vehicle back on the ground where it can be inspected and reused(in theory).
To me that's like saying all Boeing aircraft would have to land in Everett WA to be inspected and refueled after every flight. It's hard to scale a transportation system like that.
We have to get past the Apollo paradigm if we want to do more in space.
My reasons for saying that Commercial Crew vehicles are too small is that I think we have learned that for humans to stay healthy in space that they need a lot of room, so future human space travelers are not going to be spending most of their time in a capsule like the Dragon or CST-100. Plus, capsules are really only designed for transporting humans to/from a planet with an atmosphere, so at most my view is that if we take them BEO it's only for use as a lifeboat and for the "last mile" of getting humans down onto a planet. And currently the only planet we know we can land them as currently designed is Earth, so why not leave them orbiting in LEO and just plan to meet back up with them in Earth orbit on the way back?
Quote from: Coastal Ron on 10/06/2014 12:54 amMy reasons for saying that Commercial Crew vehicles are too small is that I think we have learned that for humans to stay healthy in space that they need a lot of room, so future human space travelers are not going to be spending most of their time in a capsule like the Dragon or CST-100. Plus, capsules are really only designed for transporting humans to/from a planet with an atmosphere, so at most my view is that if we take them BEO it's only for use as a lifeboat and for the "last mile" of getting humans down onto a planet. And currently the only planet we know we can land them as currently designed is Earth, so why not leave them orbiting in LEO and just plan to meet back up with them in Earth orbit on the way back?I envision for Commercial Capsule's some type of mission module that the capsule will dock to after launch similar to how the Apollo CSM docked to the LM after TLI. The mission module will be fairly light structurally since it isn't intended for re-entry. Could be even a Bigelow inflatable. The module will be discarded shortly before re-entry into Earth’s atmosphere.
Need to get over the 'discard after use' concept... is there any reason that an inflatable could not autonomously aero-break into a HEO and await reuse? The capsule could be separated and reenter while the aero-breaking of the mission module begins. We're not going anywhere if we cannot get past leaving debris trails along each mission's flight path.
I would think a careful look at cost would be in order. What would be the additional mass required to have a "mission module or inflatable" be able to aero-break in a HEO while coming back from a BEO manned mission considering the velocities involved. Not saying it is impossible but this needs to be looked at.
Sure, but that doesn't mean choosing direct return to Earth is an example of the Apollo paradigm.
I see the most promising path as commercial transport to a commercially operated LEO way station, followed by commercial transport to a waiting NASA MTV based at L1/L2 (using as many commercially available components as possible, such as Bigelow habs) which is supplied by commercially operated tankers at L1/L2, Sun Mars L1/L2 and Phobos / Deimos / LMO. Eventually, there could also be commercially operated way stations at L1/L2, Sun Mars L1/L2 and Phobos / Deimos / LMO.Aerobraking back to LEO is very difficult...
...propulsive return to LEO is expensive...
...while propulsive return to L1/L2 and direct return from L1/L2 to Earth are both cheap and straightforward. I don't see much benefit from changing to a separate LEO capsule for return, especially since the return capsule from L1/L2 can be a properly modified Dragon or CST-100.
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.
Today that works, and for a limited number of people. The challenge is that such a system doesn't scale well, and if we're not scaling then we are not going to be able to do all the things we'd all like humanity to do in space.
Ok, this is a bit off topic, but...Anybody know if anything has been done about using a generated magnetic field on a ship, interacting with Earth's magnetic field, to act as a sort of magnetic aerobraking system?If possible, it sure would save on the TPS materials on Crew Return Vehicles.
Quote from: Coastal Ron on 10/07/2014 08:08 pmToday that works, and for a limited number of people. The challenge is that such a system doesn't scale well, and if we're not scaling then we are not going to be able to do all the things we'd all like humanity to do in space.I think the only part that wouldn't be reusable would be the SM of the capsule. I suspect that could be made reusable later, and that aerobraking just a SM is easier than a whole capsule. But I wouldn't like it to be the first step, since I think it's too ambitious. As for a very ambitious long-term plan, I think NASA's OASIS architecture was very nice, except for the fact that it saw all in-space elements as traditional NASA projects, rather than commercial-crew-like competitive procurement of resupply services.
Quote from: pathfinder_01 on 10/07/2014 02:32 amIn terms of going to and from the region of the moon direct reentry to earth would probably be the best bet. It costs less in delta V and you get your vehicle back on the ground where it can be inspected and reused(in theory).To me that's like saying all Boeing aircraft would have to land in Everett WA to be inspected and refueled after every flight. It's hard to scale a transportation system like that.
Dragon shouldn't need a service module just for entering and exiting EML1/2. All you'd have is the trunk, and even that could be gotten rid o with a clever folding solar array (and/or small radiator) in the nose and/or better Li-S batteries (which are just as good as fuel cells).
Quote from: Coastal Ron on 10/07/2014 08:08 pmDragon shouldn't need a service module just for entering and exiting EML1/2. All you'd have is the trunk, and even that could be gotten rid o with a clever folding solar array (and/or small radiator) in the nose and/or better Li-S batteries (which are just as good as fuel cells).What is type of engine is providing the Delta-V change for entering/exiting EML1/2?
Quote from: RobotbeatNotCoastalRonMakeSureToEditProperlyPleaseDragon shouldn't need a service module just for entering and exiting EML1/2. All you'd have is the trunk, and even that could be gotten rid o with a clever folding solar array (and/or small radiator) in the nose and/or better Li-S batteries (which are just as good as fuel cells).What is type of engine is providing the Delta-V change for entering/exiting EML1/2?
Quote from: JasonAW3 on 10/07/2014 08:57 pmOk, this is a bit off topic, but...Anybody know if anything has been done about using a generated magnetic field on a ship, interacting with Earth's magnetic field, to act as a sort of magnetic aerobraking system?If possible, it sure would save on the TPS materials on Crew Return Vehicles.Jon Goff has talked about possible solutions that involve magnetic fields. I should PM him about this.He also wrote an article about the subject back in 2010 on his website:MHD Aerobraking and Thermal Protection Part III: Aerobraking and Aerocapturehttp://selenianboondocks.com/2010/02/mhd-aerobraking-and-thermal-protection-part-iii-aerobraking-and-aerocapture/
First, not Ron, Jason.Second, I didn't entirely make myself clear, so let my clarify.As I understand it, it is possible to create a Magnetic Sail that would allow a craft to lift itself out of Earth orbit, via the planet's magnetic field. (I read one article that suggested it may be possible to launch from teh Earth's surface with a Magnetic sail, but I think thats a bit far fetched). What I was suggestion was, as a craft is returing to Earth, use a magnetic sail as a sort of "deep space parachute" to bleed off eneough velocity of the entire craft, (Mars mission craft, habitats, engines, etc.) so that the entire craft can make orbit around the Earth and teh ERV Capsule would only have to resist the reentry from LEO rather fronm a high velocity BEO return. Obviously, using susch a system to achieve Mars orbit would be impossible, due to teh practically complete absense of a Martian magnetic field, therefor aero braking becomes a necessity. It also occures to me that a craft using a nuclear rocket is likely to also be suing some sort of Magnetic shielding to protect teh crew from solar and nuclear radiation. If so, it may be possible to use this shield as a Magnetic sail to give the craft an additional boost via Earth's Magnetic field.
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.
Quote from: Coastal Ron on 10/07/2014 07:53 pmNow 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.
I think what you are looking for is here:QuoteElectrodynamic 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
Quote from: brovane on 10/07/2014 08:24 pmQuote from: Coastal Ron on 10/07/2014 07:53 pmNow 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.
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?
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.
Only a couple of hundred m/s. That's part of why returning straight to Earth is so much easier than returning to LEO.
The low thrust of Draco isn't a concern for capturing at EML1/2.
Quote from: Robotbeat on 10/09/2014 01:53 amThe 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.
Quote from: mmeijeri on 10/08/2014 08:34 pmOnly 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.
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?
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.
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.
How is does a couple of hundred m/s imply the need for a "vastly increased propellant tanks"?
Quote from: Lars-J on 10/09/2014 07:04 pmHow 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.
This question came up on a different thread, so I thought I would start a specific one to collect everyones thoughts.The subject came up when I responded to a statement from Robotbeat:Quote from: Coastal Ron on 10/05/2014 06:46 pmQuote from: Robotbeat on 10/05/2014 03:04 pmI will say one thing: since both designs chosen were capsules, they are both relevant for any future BLEO missions and should be considered for inclusion by mission planners.None of these vehicles will be evolved for BLEO - they are too small. Be glad to talk on another thread about it if you want...A number of people agreed with Robotbeat, or at least with the idea that Commercial Crew vehicles could be adapted for beyond LEO needs.My reasons for saying that Commercial Crew vehicles are too small is that I think we have learned that for humans to stay healthy in space that they need a lot of room, so future human space travelers are not going to be spending most of their time in a capsule like the Dragon or CST-100. Plus, capsules are really only designed for transporting humans to/from a planet with an atmosphere, so at most my view is that if we take them BEO it's only for use as a lifeboat and for the "last mile" of getting humans down onto a planet. And currently the only planet we know we can land them as currently designed is Earth, so why not leave them orbiting in LEO and just plan to meet back up with them in Earth orbit on the way back?If you think Commercial Crew vehicles will be adaptable for BEO applications, please state what those applications are. For instance, would you envision using a CST-100 for visiting an asteroid or only for trips to the Moon?And if you don't think they are applicable, go ahead and state what your alternative would be.
Quote from: WindyCity on 10/10/2014 01:58 amForgive 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/
>What additional shielding would it need. It already has a water jacket to protect against cosmic rays and solar radiation.
Could they be parked in LEO and refueled as needed?What additional shielding would it need. It already has a water jacket to protect against cosmic rays and solar radiation.
The average dose-equivalent rate observed through the investigation was about 10 times the average exposure on Earth.
It takes about 600 m/s to capture at L1, or to leave L1 for Earth, with a travel time of about 5 days each way. So any capsule will have to carry an additional 1200 m/s of delta-v over what it receives from the launch vehicle. At 320s Isp, that means about 50% extra mass in propellant.For L2 it takes about 350 m/s one-way with a ~9 day travel time. So that's an extra 700 m/s, which at 320s Isp means about 25% extra mass in propellant.That's a significant amount of extra mass needed if going to a Lagrangian point and back.
That's a significant amount of extra mass needed if going to a Lagrangian point and back.
Quote from: metaphor on 10/13/2014 05:47 pmThat's a significant amount of extra mass needed if going to a Lagrangian point and back.Orion is supposed to have ~1.6 km/s in delta-v, so I don't see any problem with that.
Given that NASA is using ESA to build the service module for Orion, I rather doubt they would be as bad as Orion esp. as they could do LEO runs as well as BEO trips.
Quote from: mmeijeri on 10/13/2014 07:14 pmQuote from: metaphor on 10/13/2014 05:47 pmThat's a significant amount of extra mass needed if going to a Lagrangian point and back.Orion is supposed to have ~1.6 km/s in delta-v, so I don't see any problem with that.Well yeah, that's why the service module is there. A commercial crew vehicle would need upgrades like that, that would make it heavier and costlier, in order to go BLEO. In the end it would probably end up somewhat similar to Orion.
SINCERELY doubt it could be as expensive as Orion. The capsule dry mass is far less for Dragon and cst100, just to name one thing.
It's like putting an airport at the top of a mountain. Plane lands on an uphill runway, and stops without needing brakes, then takes off downhill without needing engines to reach takeoff speed.
Quote from: MP99 on 10/14/2014 08:19 amIt's like putting an airport at the top of a mountain. Plane lands on an uphill runway, and stops without needing brakes, then takes off downhill without needing engines to reach takeoff speed.Hey, I know that airport. Never been there, but as a former backpacking/climbing fanatic, I've read about it a number of times:http://www.weather.com/travel/mount-everest-airport-will-terrify-you-photos-20130618Had several daredevil pilots in the family too. Flew in and out of some places almost that scary with my dad.
A 4.2 km/s TMI can either be done in one burn from LEO, or ~3.2 km/s TLI + ~1 km/s post-EML. No advantage here, but no disadvantage, either.
Quote from: MP99 on 10/14/2014 08:19 amA 4.2 km/s TMI can either be done in one burn from LEO, or ~3.2 km/s TLI + ~1 km/s post-EML. No advantage here, but no disadvantage, either. Your analysis is spot on, but I think truth is even better than you suggest. There are paths to EML which combine a chemical burn for LEO departure with electric propulsion to transfer onto the EML-bound trajectory. So looking at required IMLEO, utilizing the amazingly high isp of electric propulsion for a portion of the transfer to EML can be a meaningful win.
I believe this is less true for DRO, but haven't myself done the required math. In either case, rendezvous in the cis-lunar vicinity before departure for Mars has huge mission safety advantages, because abort modes are more accessible. (With classic TMI, you have to look at each moment of a long Earth departure burn and verify there's a safe abort in case of a propulsion failure. With TMI post-EML, the burn -- and thus the vulnerability -- is shorter.)This all leads to the conclusion that EML (or DRO) rendezvous will be the Mars mission mode that one day is actually selected. Commercial crew and cargo to that rendezvous point are in the cards ... sooner or later depending on the stubbornness of those who refuse to admit it.
So looking at required IMLEO, utilizing the amazingly high isp of electric propulsion for a portion of the transfer to EML can be a meaningful win.
As long as a fuel distribution network is established first, commercial crew vehicles plus in-space habs/tugs can do it all. This is likely the reason the anti-depot crowd is adamant in opposition.
Quote from: AncientU on 10/15/2014 12:26 pmAs long as a fuel distribution network is established first, commercial crew vehicles plus in-space habs/tugs can do it all. This is likely the reason the anti-depot crowd is adamant in opposition.You don't need to establish depots first, a spacecraft can act as it own depot just as ISS and Russian stations before it have been doing for decades.
There is still no significant move within NASA towards reusable spacecraft, or even boosters, while other institutions like the Air Force and DARPA are now pushing rapidly in that direction. Funding for propellant depots is virtually nonexistent, and any refueling efforts are aimed primarily at refueling and servicing existing satellites that were never designed to be refueled. Taking another look at this document, five years after its initial release, can give us a precautionary view of where not to go in space (and Mars) mission design.
Doesn't really matter what you call it... when you have refueling technology on the (reusable) vehicles and the means to distribute fuel/refuel where and when you need it, you're good to go. Anywhere.
Quote from: AncientU on 10/15/2014 04:38 pmDoesn't really matter what you call it... when you have refueling technology on the (reusable) vehicles and the means to distribute fuel/refuel where and when you need it, you're good to go. Anywhere.Exactly, but my point is that we've had the necessary technology for years. If NASA wants to build a transfer stage, let them start with a refuelable SM and leave launch vehicles and capsules to the market by buying services competitively. Later that SM can be enlarged to a storable L1/L2 based pump-fed transfer stage for manned exploration.
I don't know I agree. People are still very skeptical about commercial crew, think that ONLY the "big boys" can do it, and at ridiculous cost and about half a century's worth of time.
Can Dragon 2 do a lunar orbit mission without modified propulsion?We know a lunar flyby with Dragon and FH is possible. The upper stage even would have enough delta-v for LOI but it won't last long enough without significant modification if at all. The idea is finding a TLI trajectory that minimizes LOI delta-v at expense of more delta-v for TLI. I am sure some modifications are possible but is it enough? It would not need a circularized lunar orbit. Just an elliptical orbit that would be easy to leave for trans earth injection too. It is not something one can take out of a delta-v map. But with plenty of abort fuel and a not so heavy Dragon is it achieavable? Ideally with enough fuel for a propulsively assisted parachute land landing.Such an orbit may not be suitable for research but would be appreciated as a tourist flight.Edit: The idea behind this is that SpaceX may not be willing to do major engineering for a modified Dragon but willing to sell a flight for a tourist operator.
Just stick a Super Draco and lots of hypergolic tanks in the trunk. But like Baldusi posted. you need longer duration ECLSS, long range communication, navigation and ground tracking & Communication network (NASA is not going to provide the DSN time).For tourism, think a free return orbit like Apollo 8 is all that is required initially.
A really, really high lunar orbit (or EML2) is probably feasible without extra propulsion (may need some light-weighting, however), if you're willing to do a week or two trip time to the Moon's vicinity.There's no "just" about adding a hypergolic stage or service module. (and you wouldn't use Superdracos, they have really crappy Isp and far more thrust than needed... instead, use an array of regular Dracos). It'd be a significant endeavor. Of course it could be done, but it wouldn't be free.
I'm CONFIDENT that this is at least the tenth time this has been discussed.
Quote from: Robotbeat on 11/25/2014 03:41 amI'm CONFIDENT that this is at least the tenth time this has been discussed.I believe you are right. I tried to avoid that by very specifically stating I am looking for a solution without modifications of propulsion. And if that is not possible just forget about it.
For tourism, think a free return orbit like Apollo 8 is all that is required initially.
Quote from: GWH on 07/27/2017 08:16 pmQuote from: ThereIWas3 on 07/27/2017 07:55 pmQuote from: GWH on 07/27/2017 07:31 pmHow anyone GETS to the lander though is anyone's guess.Some Dragon or CST-100 type vehicle?Yeah one would probably be better off discussing that in more detail here: https://forum.nasaspaceflight.com/index.php?topic=35787.100Probably wouldn't be quick and easy. Starliner is limited to 60 hour free flight, Dragon at least lacks the dV, and is a tight ride. ....False, on both accounts. And yeah, you should have discussed it in that thread.
Quote from: ThereIWas3 on 07/27/2017 07:55 pmQuote from: GWH on 07/27/2017 07:31 pmHow anyone GETS to the lander though is anyone's guess.Some Dragon or CST-100 type vehicle?Yeah one would probably be better off discussing that in more detail here: https://forum.nasaspaceflight.com/index.php?topic=35787.100Probably wouldn't be quick and easy. Starliner is limited to 60 hour free flight, Dragon at least lacks the dV, and is a tight ride. ....
Quote from: GWH on 07/27/2017 07:31 pmHow anyone GETS to the lander though is anyone's guess.Some Dragon or CST-100 type vehicle?
How anyone GETS to the lander though is anyone's guess.
At most, Mr. Ferguson stated his desire for Starliner to employ 24-hour launch to docking profiles – due in part to the vehicle’s design, which limits its free flight capability (from launch to docking and then undocking to landing) for an entire mission to just 60 hours.
Dragon 2, from information I have found, has a dry mass of 6,350 kg and carries a total prop mass of 1815 kg including the abort propellant. At an ISP of 300s for the Draco thrusters that's 0.74 km/s bone dry no payload. Well short of returning from anywhere other than L2.Now adding a kick stage of sorts or trunk based propulsion is well within possibility, but not within the scope of the vehicle as designed.
And why not stage from L2? The gateway will be in a similar energy orbit.Just because Apollo used LLO doesn't mean that we should or that it's ideal. Even Orion cannot use LLO unless it leaves LEO with a lander (or similar) attached, which tends to necessitate an expendable lander.I think EML1,2, or a similar energy orbit would be more appropriate for staging as we already have multiple current or near-term vehicles that would be capable of reaching it with minimal modifications (Orion, Dragon, Starliner, Soyuz, possibly even Shenzhou, on top of SLS, Falcon Heavy, Vulcan Heavy or Vulcan with distributed lift, New Glenn, two launch Delta IV Heavy, Proton/Angara, Long March 5, etc).As far as having enough room, Gemini was tiny and the two astronauts spent 2 weeks in LEO. 3 or so days transit (longer for a more efficient trajectory) is not a huge constraint. Dragon has much more room per crew than Gemini. Plenty for cislunar. Same with Starliner.Also, LLO is terrible for staging anywhere but the Moon.
As far as having enough room, Gemini was tiny and the two astronauts spent 2 weeks in LEO. 3 or so days transit (longer for a more efficient trajectory) is not a huge constraint. Dragon has much more room per crew than Gemini. Plenty for cislunar. Same with Starliner.
Cygnus, definitely. Dream chaser... I think so, with some work.
Quote from: Robotbeat on 07/31/2017 11:56 pmCygnus, definitely. Dream chaser... I think so, with some work.Cygnus is probably the easiest commercial vehicle to modify for BLEO use.