You are not logged in.
A I started the topic to discuss the need for cargo drops to be reuseable and what would it take to do so.....as that means 1 less lander and more per mission especially to preload a landing site......
Offline
Like button can go here
kbd512 we have had the 248Smallest Human Ascent or Descent Lander for Mars Or Earth topic or have all forgotten about it.....
So do it there.....
I'll quit advocating for advocating for single person landers when the people who advocate for using multi-person landers get serious about reducing weight and complexity, but point taken.
Even if the lander uses ADEPT and retropropulsion to accomplish deceleration and soft landing, the lander should be an unpressurized aeroshell with the absolute minimum equipment required to get from orbit to the surface. The weight and complexity extravagance should be an upressurized electric four person rover that can carry the astronauts to the habitat, if required.
Offline
Like button can go here
kbd512 if you look at the link I actually opened the other topic as a result of our discusions and I do believe that we can go much smaller than the big Nasa designs but it does come with a price as we must beat the odds of landing with the possibility of being no where near the consumables that we did not bring if we go to small.
I am reposting this into the smallest human for further discusion there please and thank you to all to do so as well.
Offline
Like button can go here
The reason that I would want to "Even if the lander uses ADEPT and retropropulsion to accomplish deceleration and soft landing" is because to get more than a single trip at a very large expense it means changing the huge mission design to make as many pieces reuseable as Falcon has demonstrated and that is how we reduce cost.
With Mars we do need to get out of that use once mentality even if its only in key spots within the mission profile.
I know that most would say that once we build the large transport ship to depart earth to get to mars porbit that that ship should be of a cycler variety or re-used multiple times after refueling in earth orbit and restocked for the next trip out.
What would be the next logical step then is to have the means to bring cargo in what we packed down to the surface without hauling another very large and expensive once use ship each time.
Offline
Like button can go here
I like the "Keep it simple" approach. I too advocate pre-landing of habs and supplies.
I can't say enough about keeping landings simple. The cost savings from simple landers means you get to spend money on things you really need to maintain a permanent human presence on Mars, like a base and pressurized rovers.
However, I am not entirely convinced of landing individuals in solo pods. Personally I feel we need to be assured the crew can rest upon arrival rather than immediately find themselves in an EVA situation. It would be better in my view if they have a couple of days' supplies with them on landing. Then one or two people, after say six hours of health and equipment checks following landing, can leave the lander and test the hab. If there is a problem with the hab (unlikely but cannot be ruled out), then the whole crew move to a pre-landed ascent vehicle and exit the scene.
There's no way to assure that EVA won't be immediately required. Use of artificial gravity aside, rigid adherence to a proper exercise regimen has been demonstrated to permit immediate mobility on Earth after a long duration space flight and Mars has substantially less gravity than Earth.
Basically I think the lander needs to be "as small as possible".
Design a crew lander or design a crew habitat, but don't transform the crew lander into a habitat. If you're that conservative in your risk reduction approach, then land the crew in a habitat.
There might be an argument for single person lander/ascent craft. So, if - say - this was a 6 person mission, you would ferry people down one at a time. The advantage then would be that the craft could be kept as small as possible. Each time the craft returned to the orbiting transit craft, it would be refuelled. It might tkae several sols to land everybody. But it might make the whole mission a lot easier to mount.
I'm not opposed to a multi-person lander at all, but its only function should be landing the crew on Mars.
Every combination lander and ascent vehicle that has progressed beyond paper uses staging. If you're shedding mass on the way down and the way up, in what way will the vehicle be reusable? A reusable Mars lander is, in effect, a SSTO vehicle that does not use staging and has been strengthened to survive multiple transits.
Offline
Like button can go here
The reason that I would want to "Even if the lander uses ADEPT and retropropulsion to accomplish deceleration and soft landing" is because to get more than a single trip at a very large expense it means changing the huge mission design to make as many pieces reuseable as Falcon has demonstrated and that is how we reduce cost.
Reusable vehicles that require no refurbishment after reentry is technology that simply doesn't exist. The MDV/MAV only has to be complicated and therefore expensive if we insist on a fully-fueled all-in-one solution to descent, ascent, and habitation. In my estimation, that will only ensure that we never execute the mission. If we're so risk averse that we can't have the astronauts walk or drive to the habitat after they land, then we land the astronauts in the habitat and call it a day.
With Mars we do need to get out of that use once mentality even if its only in key spots within the mission profile.
I agree, but a reusable descent/ascent solution is not a piece of mission hardware required for initial exploration.
I know that most would say that once we build the large transport ship to depart earth to get to mars porbit that that ship should be of a cycler variety or re-used multiple times after refueling in earth orbit and restocked for the next trip out.
If there is no requirement for the MDV/MAV solution to be immediately capable of return to the MTV, then the most massive (and therefore expensive in terms of launch costs) mission hardware elements are the Mars surface habitation modules and MTV. I hate to parrot, but ISRU makes the mission doable.
What would be the next logical step then is to have the means to bring cargo in what we packed down to the surface without hauling another very large and expensive once use ship each time.
A scaled-up sky crane like the one used to land Curiosity could potentially be refueled on Mars using ISRU and then used for ascent.
Offline
Like button can go here
On mars the MAD/MAV is reused after refueling and there is no standing army to refurbish it...that said it is reuseable but its up to the designers to figure out for just how many uses before another is needed.
The MAD/MAV is used just on the next cycle back to earth which occurs roughly 500 days later after insitu processing refuels it other wise any short term mission must already have fuel for a reload waiting and if not it must bring it with it for the emergency situation......
The sky crane could not get back to orbit even if it was refueled as its not designed to do so. Its fuel tanks are just to small for the burn time....which would then shift the mass fraction to far and it will not be able to get to orbit even with more fuel......
Offline
Like button can go here
On mars the MAD/MAV is reused after refueling and there is no standing army to refurbish it...that said it is reuseable but its up to the designers to figure out for just how many uses before another is needed.
The only way I see a reusable lander making any sense is if it can ferry multiple cargo payloads down and humans back to the MTV. The only way I see that working is if the MAV is field serviceable and spare vehicle assemblies are on-hand to replace busted components. The reentry-specific hardware must be attached to the cargo.
The MAD/MAV is used just on the next cycle back to earth which occurs roughly 500 days later after insitu processing refuels it other wise any short term mission must already have fuel for a reload waiting and if not it must bring it with it for the emergency situation......
ISRU is a hard requirement for keeping launch costs affordable.
The sky crane could not get back to orbit even if it was refueled as its not designed to do so. Its fuel tanks are just to small for the burn time....which would then shift the mass fraction to far and it will not be able to get to orbit even with more fuel......
The sky crane would have to be designed with larger fuel tanks and more powerful engines. A sky crane that could ferry four astronauts to orbit would weigh between 15t and 17t. That weight is for a vehicle carrying an unpressurized capsule. The astronauts have additional air and water in the capsule, but that's it. If you can't transfer to the MTV within 24 hours, you're a permanent resident.
Offline
Like button can go here
Just some velocity numbers for Mars entry from low Mars orbit:
Speed at entry interface is pretty near 3.6 km/s. You come out of hypersonics at roughly local Mach 3, which is in the vicinity of 0.7 km/s or a tad less. Ignoring drag decelerations of any kind from there, but at most doubling the requirement as a "pad", you have 1 to 1.4 km/s to "kill" to touch down. If you fly back to orbit, you need the entire 3.6 km/s delta-vee plus a small kitty for gravity and drag losses. That's around 4.5 to 5 km/sec delta-vee capability for a round trip, same dead-head payload mass both ways.
Assume NTO-MMH propellants with a modest engine bell in spite of the near-vacuum surface conditions. Isp near 300 sec. Exhaust velocity near 2.94 km/s. MR = 5.48 for 5 km/sec delta-vee. That's a 82% propellant fraction. This thing has landing legs and a heat shield, so you cannot have your typical modern rocket stage inert fraction of 5%. So, assume 10%. You can have dead-head payload 8% of ignition mass.
Such a thing is possible with technologies and materials we have right now, although it's unattractive: the vehicle is awfully big for the payload it carries. I'm not really sure 10% inerts is "stout" enough for re-use, but any increases in inerts must come out of payload.
Adding local refueling just makes it lots better. If delta-vee is only 1.4 for descent-only, MR = 1.61, propellant fraction = 38%, and if inerts are 10%, then payload down is 52%. Going back up refueled from the surface, delta vee is about 3.8 km/s, MR = 3.64, propellant fraction = 73%, and if inerts are 10%, then payload up is 17%.
Entering at Mars escape speed (5 km/s):
You still come out of hypersonics at about 0.7 km/s, maybe closer to the surface, though. Same 1 to 1.4 km/s to touch down. A tad over 5 km/s to escape Mars, for a total delta-vee of about 5.5 to 6 km/s for a two-way vehicle. At 6 km/s, MR = 7.70, propellant fraction is 87%, and with 10% inerts, payload is only 3% at best. So, in practical terms, we must have either higher Isp or refueling on the surface to accomplish this. If we don't have those items in-hand and ready-to-use, then we cannot accomplish the mission.
A one-way descent-only vehicle looks just like the LMO-based version, because you come out of hypersonics at the very same M3 speed. That you can do. But if surface-refueled for an escape ascent, delta-vee is a tad over 5 km/s minimum, say 5.3. MR= 6.07, propellant fraction = 84%, and if inerts are 10%, payload is at most 6%. This is about as "bad" as the two-way un-refueled design for an LMO-based mission.
There really is a technical advantage to basing your mission out of LMO, and using reusable "landing boats" to enable visiting multiple sites. There is also a strong strategy reason to do it that way, too.
Just going to one site is about halfway back to nothing but a flags-and-footprints mission, at least. I have to ask the question: what's the point of going to all the trouble and expense to reach Mars, if you don't really explore it? The lesson learned over the millennia here at home is that no two sites are ever alike.
In my opinion, just visiting one site is flags-and-footprints nonsense. That pretty much rules out the direct-type missions. If you base from LMO, then build a real landing boat. And go exploring multiple sites. If in-situ refueling actually works at high production rates, then you get to explore a whole lot more sites.
GW
Last edited by GW Johnson (2016-01-07 12:30:09)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
Offline
Like button can go here
Just some velocity numbers for Mars entry from low Mars orbit:
Speed at entry interface is pretty near 3.6 km/s. You come out of hypersonics at roughly local Mach 3, which is in the vicinity of 0.7 km/s or a tad less. Ignoring drag decelerations of any kind from there, but at most doubling the requirement as a "pad", you have 1 to 1.4 km/s to "kill" to touch down. If you fly back to orbit, you need the entire 3.6 km/s delta-vee plus a small kitty for gravity and drag losses. That's around 4.5 to 5 km/sec delta-vee capability for a round trip, same dead-head payload mass both ways.
The sky crane I had in mind can manage a 5.2 km/s Dv.
Dropping cargo on an inverted ADEPT device rather than soft landing it was about improving fuel economy.
Assume NTO-MMH propellants with a modest engine bell in spite of the near-vacuum surface conditions. Isp near 300 sec. Exhaust velocity near 2.94 km/s. MR = 5.48 for 5 km/sec delta-vee. That's a 82% propellant fraction. This thing has landing legs and a heat shield, so you cannot have your typical modern rocket stage inert fraction of 5%. So, assume 10%. You can have dead-head payload 8% of ignition mass.
I did assume NTO and MMH propellants with engines that have extendable nozzles and an Isp of ~340s, but I assume comparable methalox engines could be developed with similar Isp and the advantage of refueling using ISPP on Mars.
Such a thing is possible with technologies and materials we have right now, although it's unattractive: the vehicle is awfully big for the payload it carries. I'm not really sure 10% inerts is "stout" enough for re-use, but any increases in inerts must come out of payload.
The sky crane won't land with the payload, so the landing gear can be significantly lighter and still be robust enough for reuse.
Adding local refueling just makes it lots better. If delta-vee is only 1.4 for descent-only, MR = 1.61, propellant fraction = 38%, and if inerts are 10%, then payload down is 52%. Going back up refueled from the surface, delta vee is about 3.8 km/s, MR = 3.64, propellant fraction = 73%, and if inerts are 10%, then payload up is 17%.
As previously stated, I assume refueling on Mars.
Entering at Mars escape speed (5 km/s):
You still come out of hypersonics at about 0.7 km/s, maybe closer to the surface, though. Same 1 to 1.4 km/s to touch down. A tad over 5 km/s to escape Mars, for a total delta-vee of about 5.5 to 6 km/s for a two-way vehicle. At 6 km/s, MR = 7.70, propellant fraction is 87%, and with 10% inerts, payload is only 3% at best. So, in practical terms, we must have either higher Isp or refueling on the surface to accomplish this. If we don't have those items in-hand and ready-to-use, then we cannot accomplish the mission.
Surface refueling is what makes the solution practical. If we can't do that, it's impractical.
A one-way descent-only vehicle looks just like the LMO-based version, because you come out of hypersonics at the very same M3 speed. That you can do. But if surface-refueled for an escape ascent, delta-vee is a tad over 5 km/s minimum, say 5.3. MR= 6.07, propellant fraction = 84%, and if inerts are 10%, payload is at most 6%. This is about as "bad" as the two-way un-refueled design for an LMO-based mission.
Ok
There really is a technical advantage to basing your mission out of LMO, and using reusable "landing boats" to enable visiting multiple sites. There is also a strong strategy reason to do it that way, too.
My mission architecture puts the MTV and all surface hardware sent ahead of the MTV in LMO first using SEP. The MTV uses a chemical kick from L1 and spirals in to LMO using SEP. I think aerobraking the MTV is insane and aerobraking cargo only slightly less so.
All cargo should be shipped using SEP tugs. It doesn't have to get to Mars fast, it just has to get there.
Just going to one site is about halfway back to nothing but a flags-and-footprints mission, at least. I have to ask the question: what's the point of going to all the trouble and expense to reach Mars, if you don't really explore it? The lesson learned over the millennia here at home is that no two sites are ever alike.
Your statement is the reason why my mission architecture puts the astronauts in a convoy of pressurized surface rovers with real mobility and durability. M113's are durable vehicles. The tin can on wheels approach that NASA wants to use is neither durable nor particularly mobile. Real Mars surface exploration means a road trip in vehicles specifically designed for off road use.
In my opinion, just visiting one site is flags-and-footprints nonsense. That pretty much rules out the direct-type missions. If you base from LMO, then build a real landing boat. And go exploring multiple sites. If in-situ refueling actually works at high production rates, then you get to explore a whole lot more sites.
GW
Rather than attempting to fly around Mars on expensive, complicated, and failure prone rockets, use pressurized surface rovers instead. The M113 is not as sexy or high-speed as a rocket powered lander, but it will get the job done.
Offline
Like button can go here
SpaceNut,
I base my information on the mass of a sky crane with the required performance characteristics to both propulsively land cargo and carry the crew back to the MTV from work done by Scott Alan Geels as part of his master's thesis in 1990.
System Design of a Mars Ascent Vehicle by Scott Alan Geels
I think pump fed methalox engines built using the latest and greatest in materials and design would improve on mass and Isp over the Space Shuttle AJ-10-190 derivative that Mr. Geels used in his thesis as the basis for a reusable or user serviceable propulsion system for the sky crane.
Mr. Geels MAV design is what I consider to be an unnecessary mass design for carrying the astronauts back to the MTV. Put the astronauts in an unpressurized capsule with water and oxygen. Nothing more extravagant is required and anything more complicated than that simply introduces more failure modes at greater cost. Each and every attempt to increase safety beyond use of a practical and simple design approach will only ensure that the mass and complexity of the solution are so great that there is insufficient funding to implement it.
Offline
Like button can go here
Thanks for the link kbd512, gee 196 pages at a first glance the MAV is a minimal approach as it has only 38 hrs to catch the MTV and has no loiter time on the launch pad.
I also see that its a two stage with the base using hydrogen to land with which allows for a higher payload to the surface while using storable fuel for ascent not using any insitu resources for refueling. I will need to read the total document but I get the impression that there is no payload cargo coming back.
One more reason for the over sized stage is the hydrogen boil off before we will even get to use it to land the crew in.
Offline
Like button can go here
GW I got wondering about the New Shepard sub orbital craft as to whether it would be possible with small modifications with regards to using it as a mars lander. I would assume that a pica heat shield would be one of those items but its intended to be a quick useage vehicle so no need for life support to be much more than a few days as in kbd512's posted link....
Offline
Like button can go here
Thanks for the link kbd512, gee 196 pages at a first glance the MAV is a minimal approach as it has only 38 hrs to catch the MTV and has no loiter time on the launch pad.
Although Mr. Geels MAV solutions were designed for a slightly different purpose, and decades ago, it should be relatively clear that a reusable sky crane is simply not going to carry much payload with it to orbit. My intention is to use a minimal cost and complexity unpressurized capsule design with minimal safety equipment and consumables required to get the astronauts and samples back to the MTV. It's a one-shot deal. You get it right or you don't come home.
I also see that its a two stage with the base using hydrogen to land with which allows for a higher payload to the surface while using storable fuel for ascent not using any insitu resources for refueling. I will need to read the total document but I get the impression that there is no payload cargo coming back.
A multi-stage vehicle is impractical for reusability on Mars. In fact, if ballutes of sufficient size to land heavy cargo are successfully demonstrated, I see few scenarios where the cost and complexity of a reusable MDV/MAV makes sense.
One more reason for the over sized stage is the hydrogen boil off before we will even get to use it to land the crew in.
Too much non-existent infrastructure is required to use LH2 on Mars.
Offline
Like button can go here
Link page 26 indicates hydrogen fuel and continues the choice selection of fuels on page 45 forward.
The link is no sky crane and that belongs in the other topic.
I do agree that we need to make things as lite as possible but not at the sacrifice of crew or mission.
Is there a place for both vehicle types, I do believe so but at what stage of mission are we to introduce each is the question.
The disposable methods of nasa's use once especially for mars landings does cost as indicated it takes a factor of nearly 20 times that to which we deliver to mars versus what we need to push it into orbit. Now that is costly....
So yes we do need a minimalist landing capability ( in smallest landing ascent vehicle) and also one that is larger for other purposes. So be it that if we do want a small lander lets talk about that in that topic....
Offline
Like button can go here
Link page 26 indicates hydrogen fuel and continues the choice selection of fuels on page 45 forward.
The link is no sky crane and that belongs in the other topic.
Are we talking about Mr. Geels MAV thesis or something else?
If we are talking about the thesis, maybe my copy of it is different. Page 26 has a diagram of a NTO/MMH powered MAV.
Page 45 shows that LOX/LH2 has the best Isp of the fuels considered, but his recommended design used storable hypergolics and pump fed engines. I would replace the NTO/MMH with pump fed LOX/LCH4. The study indicates that much larger fuel tanks are required to account for the lower density of LH2 and that LH2 boil off has to be resolved for LH2 to be suitable for use on Mars. To this day, boil off has not been resolved. NASA is still working on it.
Regarding the sky crane concept, take the capsule off the MAV, attach landing gear, and mate it to a piece of cargo equipped with its own heat shield (ADEPT). Then you have a sky crane. The device has enough lift capability to take 4 suited astronauts back to the MTV and enough thrust to propulsively land moderately sized cargo elements.
I do agree that we need to make things as lite as possible but not at the sacrifice of crew or mission.
We're not sacrificing anything but funding by designing a dual purpose reusable lander. It's a good idea, but at what cost? I would attempt all workable passive EDL methods first before spending a dime on a reusable lander.
Is there a place for both vehicle types, I do believe so but at what stage of mission are we to introduce each is the question.
The cost of a reusable lander won't make a handful of exploration missions more economical. A reusable lander may be required for settlers, but that's many decades down the road. We need to demonstrate we can go there and come back before we concern ourselves with more advanced hardware for more sophisticated missions or colonization.
The disposable methods of nasa's use once especially for mars landings does cost as indicated it takes a factor of nearly 20 times that to which we deliver to mars versus what we need to push it into orbit. Now that is costly....
That means the support infrastructure required to use a reusable spacecraft on Mars will cost substantially more, too. Reusability doesn't work without a fully functional ISPP setup on the surface of Mars.
So yes we do need a minimalist landing capability ( in smallest landing ascent vehicle) and also one that is larger for other purposes. So be it that if we do want a small lander lets talk about that in that topic....
I'm not married to the idea of sending individual astronauts to the surface, but I am married to the idea of minimal cost and complexity designs for every major piece of mission hardware.
Offline
Like button can go here
Ah pg 26 Hyd was not Hydrogen but was hydrazine for the thrusters.
The normal MAV must be refueled on the surface as it uses up all of its fuel to land empty with no crew or cargo.
With a seperate habitat descent (MDV) stage that has the crew with supplies that make it very heavy.
This thesis does not and that is why it has a descent stage (MDV) which is much larger as it must bring down the fully loaded Mav's fuel supply and the crews habitat space as well. The capsule on the Mav is to protect the crew on descent and ascent as it seperates from the rest of the MDV on return to orbit after the mission is done leaving the habitat behind on the surface.
Offline
Like button can go here
Ah pg 26 Hyd was not Hydrogen but was hydrazine for the thrusters.
Correct.
The normal MAV must be refueled on the surface as it uses up all of its fuel to land empty with no crew or cargo.
Perhaps my math is completely wrong, but landed payloads should be ~20t. That's at or near the limit of what one Falcon Heavy and a SEP tug can reasonably send to Mars.
The exact MAV design Mr. Geels proposed can't be used, but something in that weight class (15t-20t), should be capable of landing 20t payloads equipped with ADEPT and a parachute. 5.2km/s should be enough dV to enter a low orbit, capture the cargo, de-orbit, and kill 1 - 1.4 km/s velocity during the terminal phase of the descent.
Four Falcon Heavy rockets send two sky cranes to Mars using SEP tugs.
Sky Crane #1 (SC1) Payload:
SAFE-400 reactor
power distribution equipment
Replacement sky crane components
Robot #1 (R1) - Earth Mover
Robot #2 (R2) - Depot Deployment and Repair
Robot #3 (R3) - Depot Operations
Sky Crane #2 (SC2) Payload:
ISPP device
propellant distribution equipment
Depot Setup
Depot Setup Sequence:
1. SC1 lands
2. R1 digs a pit for the reactor
3. R3 emplaces the reactor
4. R2 connects power distribution equipment
5. R1 digs a pit for the ISPP depot
6. R1 digs pits for the sky cranes to land in
7. SC2 emplaces the depot in its pit and then lands in one of the pits dug by R1
8. R2 connects power distribution equipment to the ISPP depot
9. ISPP depot operations begin (plant starts converting gelled hydrogen into LOX and LCH4)
10. SC1 moves to its pit.
11. R2 determines the serviceability of SC1 and SC2, replacing damaged assemblies with components from the spare parts box.
12. R3 refuels SC1 and SC2
Subsequent Falcon Heavy rockets send pressurized rovers, inflatable habitat module, and consumables using SEP tugs.
Depot Operations Sequence:
1. Cargo arrives in LMO.
2. SC (1 or 2) ascends to orbit, fully fueled.
3. SC mates with cargo.
4. SC de-orbits the cargo.
5. SC drops or soft lands the cargo.
5. SC returns to the refueling pit.
6. R2 inspects the SC and repairs it, if necessary.
7. R3 refuels the SC.
With a seperate habitat descent (MDV) stage that has the crew with supplies that make it very heavy.
The sky crane is a single stage vehicle that's normally only pushing itself or very little payload (unpressurized capsule) to orbit. The landed payloads are obviously much heavier, but our sky crane is also much lighter when reentry occurs because it had to push itself to orbit to begin with.
It's designed to provide a 5.2km/s dV for a fairly substantial capsule and reach a 250km orbit. Mr. Geels entire vehicle weighs 15t, including the pressurized capsule. A similarly sized vehicle with no capsule (apart from when a capsule is attached to return the crew to the MTV) should have enough dV remaining to de-orbit its cargo and kill remaining velocity for a soft landing after ADEPT and parachutes have killed most of the initial velocity.
This thesis does not and that is why it has a descent stage (MDV) which is much larger as it must bring down the fully loaded Mav's fuel supply and the crews habitat space as well. The capsule on the Mav is to protect the crew on descent and ascent as it seperates from the rest of the MDV on return to orbit after the mission is done leaving the habitat behind on the surface.
I think we're talking about doing different things here.
The sky crane has to land a heavy payload, but I think Mr. Geels MAV design has roughly enough load bearing capability, thrust, and fuel to do that. His MAV had to survive reentry with a 1.5t worth of payload atop the MAV's support structure, with 5G sustained loads and 10G peak loads. Our sky crane variant sits atop its payload and weighs substantially less than his fully loaded MAV upon reentry.
The cargo attachments and structure of the sky crane have to support the full weight of the cargo when retropropulsion starts and account for loading during reentry. We would have to beef up his design a little and add landing gear, using stronger and lighter materials, hopefully. Our lighter and more efficient methalox engines generate more thrust. Our tankage volume and therefore mass is not substantially different because the bulk density of NTO/MMH and LOX/LCH4 is not that different. Our payload to orbit requirement is ~1/3 of his requirement. We're only taking a payload to orbit when we're carrying the astronauts back to the MTV.
Offline
Like button can go here
I typically will use comparison scaling when I look to what we have and what we want to do with it.
So lets look at the Falcon 9 heavy which can lift 53 mT to earth orbit and when I look at the same rocket being launched from mars surface we can scale it down by a factor of 2.66 as mars is only 0.375 that of Earth for gravity.
Or even think of it this way when we launch a falcon 9 v1.2 FT we can loft to orbit 22.8 mT so if this was setting on mars and scaled down by the 2.66 factor then we have a payload of ~8.6 mT which is approximately the size of a red Dragon. Normally its 70 m tall for payload and both stages. Which suggests a scaled down height of ~26.5 meters which is a long way to the ground from a capsule door but that could change as we work through the stage numbers. The Dragon Spacecraft & Trunk 8.1m (26.6 ft) height. Payload flairing is 5.2 m tall but I think we can use the dragons height once we recalculate the stages under the capsule changes.
Since Mars is a near vacuum it only makes sense to configure the lander with the correct engine (934 kN (Vacuum) Merlin Burn time of 397sec) for this iteration of design meaning we need for the second stage only ~351 kN for mars. Which means only 3 engines are required.
The normal first stage engine at sea level, for a total thrust of 6,804 kN ( Merlin 1D burn time 162sec) means we need to target ~ 2,560 kN for launch from mars surface for 1st stage. One engine is only 756 kN so giving the new first stage the 934 kN (vacuum engine) only makes sense.
Current Space x page indicates first stage Thrust At Sea Level 7,607 kN Thrust In Vacuum 8,227 kN, which appears to be 47 m tall. Mars height would be 17.7 m tall for the stage. Normally both stages plus flairing is 70 so if we remove the Pay load flairing height of 5.2 m out of the 70 m and 47 m first stage then the second stage is 17.8 m tall for the falcon 9 rocket and for mars at ~ 6.7m.
Merlin Vacuum Certification On March 7, 2009, SpaceX performed a full mission duration firing of the new Merlin Vacuum engine at McGregor. The engine fired for six minutes or 360 seconds, consumed 45.36 tonnes of propellant, and demonstrated a vacuum specific impulse of 342 seconds, highest ever for a U.S. hydrocarbon rocket engine.
The two-stage, 313 tonne, kerosene/LOX rocket so proportional for mars means ~118 t of fuel and oxidizer.
The second stage normally fires for 397 sec. so probably close to 50 t for the stage and for mars its 18.8 t.
The first stage then calculates to 263 t of which for reusuability is about 70 % leaving the rest for landing. So if we were on orbit and coming down then we would need ~79 t so for a retropropulsion we need ~ 30 t to land not count stage and capsule mass plus on orbit.
So mars sized falcon 9 is 32.5 m tall for a dragon plus truck of 8.1 m with a first stage 17.7 m with fuel/oxidizer of 30 t with a second stage that is 6.7 m tall and fueled with 18.8 t of which we would need to land with the second stage empty and a bit large fuel fill for the first stage for th combined landing attempt.
Seems like we could make this a single stage to orbit with the 9 vacuum engines.
Of course as meantioned the RP-1 and Lox is not the correct fuel for mars if we are making insitu fuels so now we would redo these calculations for the new fuel type and engines that we could use.
Something else is to change the 3.7 m diameter to the more practical 10 m to make the stages shorter as well.
With this long post we can see that for mars we are only landing a stackup of no more than the hieght of the current stage Falcon 9 for the entire mars lander. Which is a small 40 m tall at the 3.7 m diameter but if we go to the 10 m diameter then we are looking at something under 15 m tall. That said 4 engines for a complete single stage to orbit would seem to be correct.
So now to covert for the methane-lox and engines for the same scaling once engines numbers are looked up.
While we could land with NTO-hydrazine we do not have an insitu ability developed yet for manufacturing it for refueling.
The same holds true of NTO / MMH even with the super Draco engines.
We really need the ability to make other insitu fuels so as to be able to use what we have rather than changing plans for what we need developement for.
https://en.wikipedia.org/wiki/Dinitrogen_tetroxide
Nitrogen tetroxide is used as an oxidizer in one of the more important rocket propellants because it can be stored as a liquid at room temperature. Nitrogen tetroxide is made by the catalytic oxidation of ammonia: steam is used as a diluent to reduce the combustion temperature. In the first step, the ammonia is oxidized into nitric oxide:
4NH3 + 5O2 → 4NO + 6H2O
Most of the water is condensed out, and the gases are further cooled; the nitric oxide that was produced is oxidized to nitrogen dioxide, which is then dimerized into nitrogen tetroxide:
2NO + O2 → 2NO2
2NO2 ⇌ N2O4and the remainder of the water is removed as nitric acid. The gas is essentially pure nitrogen dioxide, which is condensed into dinitrogen tetroxide in a brine-cooled liquefier.
https://en.wikipedia.org/wiki/Monomethylhydrazine
Monomethylhydrazine (MMH) is a volatile hydrazine chemical with the chemical formula CH3(NH)NH2.
Offline
Like button can go here
based off from this post http://newmars.com/forums/viewtopic.php … 01#p139501 and this one http://newmars.com/forums/viewtopic.php … 42#p139542 and GW's post http://newmars.com/forums/viewtopic.php … 33#p139633
it is not ony probable but is in the capability of current Space X design methods as well as others if they duplicate them....
Offline
Like button can go here
Change the word Mars to Moon and elsewhere in the topic and it applies to the new thinking of reuse and not of disposal after one use.
Offline
Like button can go here
Little did we know that the Starship is just this topic but only much larger.
Offline
Like button can go here
Trooling for topics and here is Reusable Rockets to Orbit who knew we would be looking at the starship before its name and concepts were even on a drawing board....
Offline
Like button can go here
The skycrane is simular to the super draco retro rockets only that they stay with the machine. GW ran the numbers and the Red dragon could land but in no way could it return to orbit.
Lets say we dump the outer shell of the dragon and make it more like the sky crane in that its dumped. That the remaining vehicle has a hydrogen or methane engine and small tanks. That the vehicle can have detachable or drop tanks built insitu on mars for the fuel that we would use.
Offline
Like button can go here
While this might be the lowest of energy for mars surface back to orbit how do we refuel when we use LCO and LOX on orbit.
Going forward its a puzzle that must be over come as we do not make engines to use that many different fuels and most are not even adjustable between Hydrogen and Methane to say nothing about the engines which use the hydrogel fuels....
Offline
Like button can go here