New Mars Forums

Viking was big and heavy and nothing but rocket braking to landing,  all the way from the end of atmospheric entry.  I don't see why that can't be scaled up to any size.  Might not be the lowest propellant mass,  but we already know it worked twice in a row back in 1976. 

GW

Launches of Falcon-Heavy from Vandenburg AFB in S California are more-or-less southward over the Pacific for more-or-less polar orbits.  Very popular for military stuff,  not useful at all commercially.  Spacex's pad at Vandenburg will be mostly for USAF payloads as the customer on Falcon-Heavy.  Those are typically 25+ ton payloads,  what the shuttle bay was originally designed to carry. 

Polar-only at Vandenburg is why Spacex trying to buy the old shuttle pad at Canaveral,  to support eastward launches of Falcon-Heavy at about 23 degree inclination.  That's what the LEO 23 deg 53 ton figure is for.  That's for both NASA and commercial payloads.  But,  Canaveral is pretty much governed by NASA rules and bureaucracy.  If they can obtain the pad,  that'll be their first available eastward launch site for Falcon-Heavy.

They're also looking for a purely commercial launch site,  where only FAA approval is required,  unhampered by NASA bureaucracy,  for purely commercial launch services.  The candidates are all eastward launch for the more-or-less 23 degree inclination,  supporting commercial needs.  Far south Texas is the one I'm rooting for.  Near Brownsville at the mouth of the Rio Grande.  Out over the Gulf of Mexico into the mid-to-south Atlantic. 

The cost per pound-or-kg delivered payload can be deceptive.  They are usually calculated as launch cost divided by max payload capability.  But,  if the rocket doesn't fly fully loaded,  launch cost is usually the same or not very much different,  while payload weight can be very much smaller,  leading to a very much higher unit cost.  You get the full cost benefit only if you fly fully loaded. 

I noticed a new,  slight price break being projected for Falcon-Heavy on Spacex's website:  below 6 tons,  $85M,  but from 6 tons to the max 53 tons,  $124M.  I might be off a trailing digit or so,  but those figures are pretty close to what I read a couple of days ago.  The unit cost at 6 tons is bunch higher.  It really pays off to fly at or very near full load at 53 tons.  Metric tons,  that is.  Right at $1000/lb. 

Figured at launch cost divided by max payload,  I had right at $2500/lb for Falcon-9 at its 10.45 tons.  Shuttle was 1.5B per launch,  25 metric tons max,  which was about $27,000/lb.  Multiply those figures by 2.205 for $/kg.  I can't remember what I had figured for some of the Atlas-V and Delta-IV configurations,  but those data are posted over on "exrocketman" in the last few days. 

GW
http://exrocketman.blogspot.com

The old 1959-ish designs from the original Project Orion were smaller.  If memory serves,  their big one was a 10,000 tonner for going to Saturn and back in (only!!!) 3 years,  stopping off at the moon and Mars along the way!  It used shaped-charge fission devices,  at about 1 per second. 

You use low-yield fractional kiloton devices for surface launch,  where the blast wave helps push you,  then a few kilotons each,  once out in space where it's pure radiation pressure.  Again,  if memory serves,  that design was in the 2-to-4 gee range during the "burn".  Then in coast,  it just spun about its longitudinal axis for artificial gravity.  A 2-to-4 gee "burn" measured in a day or two,  is quite doable for some very high interplanetary travel speeds.  Months instead of years to Saturn,  for example. 

Myself,  I'd be afraid to try to land a thing like that directly upon a planetary surface.  Launch,  yes.  Land?  Jeez,  how do you keep it controlled that fine?  If it were me today,  I'd have rocket landing craft aboard,  to make the surface visits.  Being nuke anyway,  I'd just use a hell-for-stout-built single stage "boat" powered with a close variant of the old NERVA solid core nuke thermal rocket.  That's good enough for single-stage two-way on Mars,  Mercury,  or any of the outer moons.  At 10+% payloads. 

GW

Rune:

You did a really good job thinking about a lot of really tough issues on that one. 

There's a lot of pulse propulsion information buried in George Dyson's book "Project Orion:  The True Story of the Atomic Spaceship".  George is the son of famous physicist Freeman Dyson (who did work on old USAF "Orion").  The "cover" to get funding as a USAF project was an "orbital bomber".  But that team clearly had deep space exploration travel as their goal,  the whole way.

There's a whole slew of famous folk who worked on that project who couldn't talk about it until recently.  Who they were and what they did will really surprise you.  What eventually happened to it will disgust you.  As it did me. 

You're exactly right about the nuclear "shaped charges",  that's exactly how to get a spindle shape of EM radiation pulse from the explosion.  In space there is no blast wave at all,  just that pulse of intense EM radiation.  If it's spindle-shaped,  your pusher plate can be made to intercept one end (half) of it,  at the design detonation distance.  It's a diameter-at-range thing (constant angle).

Until one looks at actual nuclear test results from Nevada in the 50's,  one would think this radiation pulse would vaporize the steel pusher plate,  but it does not.  If you grease the plate,  the steel is completely un-eroded even for multiple explosions (sacrificial very thin layer of grease,  replenished after the "burn" to be ready for the next one). 

Your L/D proportions for spin about the longitudinal axis matches old Orion's typical ship shape and dimensions.  It was my long Mars "stacked module" ship that spun the other way:  end over end.  Both are dynamically stable,  and extremely simple.  Short and fat works best with pulse propulsion. 

I'm guessing that the shaped charge effect can be done with thermonuclear devices (all they did back then was fission).  If so,  then gigantic pulse ships like yours become easy to build.  We already know it works.  The old Orion guys flew a 1-meter model just fine with ordinary explosive charges long ago.  Even though they weren't supposed to.

The only real problem would be EMP wave effects from the explosion damaging electrical stuff near enough by to be hurt (it is a 1/r^2 decrease with range,  like ordinary radio).  I doubt very seriously we would really want to start one of these from low Earth orbit routinely.  But maybe a few thousand miles up would work fine.  10 times more r is 1/100 times the EMP intensity. 

Even with fission devices,  the fallout from surface-launching a fairly big ship is about like popping one typical ICBM weapon warhead in the atmosphere.  Spread over a period of a few years,  I think we could easily afford the radiation fallout from launching a half dozen of these.  The real problem is EMP during the launch.  The "shipyard" needs to be very isolated,  like way out in the Pacific,  maybe.  I dunno. 

Imagine what we could do with anywhere from 1 to 6 of these in the 10,000-100,000 ton range of size:   plant major colonies anywhere in the solar system,  in a single trip.  And your 10,000,000-100,000,000 ton size range actually could be a slowboat multi-generational starship. 

The hardest thing about your starship isn't the ship or its propulsion,  it's the closed ecology life-support,  and the organized "miniature industrial society" setup to maintain all the technologies and hardware and pulse "fuel" for centuries.  We get those items down right,  and multi-generational interstellar flight becomes a realistic thing to consider doing.  We may even have some reliably-identified more-or-less-Earthlike target exoplanets to visit,  by the time we get that support stuff "right",  if we started right now and worked on it (but,  we are not doing those things). 

I think you're much younger than I am,  being bothered by "exams".  That's over 4 decades ago for me.  You might actually live to see one of these pulse ships built,  if the politics changes to support it.  I probably won't.  I'll be lucky to live to see a manned Mars mission of any sort.  Maybe not,  the way things are going right now.

But hope springs eternal....

GW

All the Dragon data that I have seen says there is 1290 kg (1.29 metric tons) of hydrazine and NTO in the capsule itself,  without the trunk.  You have to shed the trunk to use the heat shield.  No trunk during powered landing (but there are landing legs adding to the inert mass!!!).

Figure a capsule around 5 or 6 tons,  with 1.29 tons of fuel.  Use about 307 Isp for hydrazine/NTO in near-vacuum,  but knock your theoretical delta-vee down by a multiplicative factor of 0.71 for the cant angle of the Super Dracos.  Even with a parachute assisting during the last part of the descent,  that's really pushing a successful landing. 

That kind of delta-vee is entirely insufficient for an ascent,  even if fully refueled on the surface somehow.  You've got gravity and drag losses cutting it further (I'd hazard a guess of a 1.05 divide-by knockdown factor for 0.38 gee and very thin "air").  You still have the 0.71 cosine multiplicative knockdown factor for the cant of the nozzles. 

Dragon might serve as the manned cabin on something much larger.  It just can't do the two-way lander job all by itself.  Rocket equation physics simply precludes that.  If Musk is planning to use Dragon as part of a manned lander,  then he has a big landing stage,  or multiple stages more likely,  up his sleeve that we haven't seen yet.  (Or maybe he doesn't.  Yet.  But he will.)

There's another company out there that I personally know hasn't revealed everything they want to do just yet.  I'm supposed to help them do it when the time comes.  I suspect all the rest are similar in their secrecy about plans and schemes. 

GW

Glad you liked the data,  Louis.  I worked hard on that,  to make sure it was both usable and reliable. 

As soon as there is a reliable lander,  I'd bet Musk will scrape up the money and go to Mars,  without NASA if he has to.  But the lander is the missing tinkertoy in our toybox,  as far as Mars is concerned. 

Exactly what kind of a lander you build depends in great part upon your basic mission architecture.  For first-visit explorations,  I just don't see the sanity of sending the Earth return vehicle to the surface of Mars.  That's the same weight penalty that almost forced Apollo into a two-launch-one mission architecture.  Doing a lander ("lunar orbit rendezvous") made the moon shots do-able as one launch-one mission.  That was fortunate,  because back then,  orbital assembly by docking was beyond our reach.  Docking capsule with lander was a stretch,  back then. 

There are serious difficulties landing things over about half a ton on Mars.  Aerobraking is not sufficient because the "air" is just too thin,  yet thick enough for significant entry heating.  It simply takes rocket braking,  and that means propellants and stages if chemical.  Yet,  it has to be clean aerodynamically,  and it has to have a heat shield.  It cannot be built flimsy and light,  like the Apollo LEM.

Unlike the moon,  there's enough gravity on Mars to put a two-stage rocket-braker out of reach with chemical propellants.  Three or more stages makes for a very large vehicle with a fixed payload mass and volume.  Tiny things like a small sample return we can design,  but how big a thing does it take to carry 1-6 men to Mars orbit?  That's huge!

I think the lander is the critical design issue.  Orbit-to-orbit ships we can build.  It's that lander that drives things to distraction.  That's the solution we lack.

I suspect you could do it single stage rocket burn descent and ascent with a NERVA-like solid core nuke and LH2.  (I'd really like to see a water nuke,  but nobody ever built one.)  Single stage landers can be made refuellable and reusable.  That opens up a whole new slew of mission design possibilities.   

The government has a monopoly on things nuclear here in the USA.  If ever there was a critical enabling technology needed to send men to Mars,  it is a practical Mars lander.  Single stage nuke is the practical one,  or so it seems to me.  So why is NASA screwing around with a gigantic shuttle-derived launch rocket,  when a practical lander is what we really desperately need?

I hate how politics has killed what once was a shining example of a government agency. 

GW

I doubt the wisdom of building something arbitrarily to the shape of a science fiction design.  But,  I like the idea of building an orbit-to-orbit transport of some kind.  That idea makes a great deal of sense.  You add a "landing boat" for visiting the surface,  if needed. 

Based on what we currently and demonstrably know how to do,  I think that such a craft craft would be assembled from cylindrical docked modules,  like the ISS.  I also think that the habitable volume will be very small compared to the propellant volume,  based on propulsion we know how to do and have done,  at one time or another. 

I rather think the ship we might build will be a slender linear stack of modules with habitat at one end and engines at the other,  more like the "Discovery" in the movie "2001 A Space Odyssey".  Except,  rather than building a centrifuge inside the habitat,  it would be easier just to spin the ship end-over-end,  while in coast,  to provide one full gee at the habitat module,  at very low rpm,  and with no bearings or anything else to worry about.  Short term exposures to zero gee while de-spun for maneuvers should be no problem at all. 

As for propulsion,  with chemical rockets,  the propellant volume is huge,  and empty tanks will have to be staged off.  The rocket equation evaluated at realistic mass ratios confirms this.  It is even true for LH2-LOX,  the very best we have.  The trip is a "slowboat" minimum-energy orbit of 7-9 months one-way.  That cannot be avoided.  Given the wait for orbits to be right for return,  this is about a 3 year mission.

4 decades ago we came within about a year of flying a solid-core nuclear thermal rocket engine called NERVA that used LH2 for propellant.  It has been forgotten to death,  and slandered with irrational fears,  ever since.  Using that technology,  a modular Mars vessel is 3-4 times smaller.  But it still must stage off empty tanks,  and it must still fly by the "slowboat" min energy orbits.  It's still about a 3 year mission.

The kind of propulsion we need for the fast trajectories does not yet quite exist in a usable form.  Claims have been made about trips anywhere from 30 to 90 days one way using ion or VASIMR electric schemes.  These have the specific impulse,  but not the thrust per unit engine weight to pull that kind of a trip off.  Basically you get a thrust measured in single-digit pounds for an engine system weighing tons,  mounted in a vehicle weighing dozens to hundreds of tons.  Just the getaway from LEO is months long.  Whether you use nuclear or solar power,  a MW-class electric generator is simply going to weigh many,  many tons.

It might be wiser to put high-thrust chemical or nuke rockets for the getaway and arrival burns,  and apply the electric stuff to speed up the coast in between.  That might actually help.  In that case,  a slowboat mission might be done without staging empties off.  Maybe even a bit faster. 

There are some other concepts that might provide higher thrusts for the weight at high specific impulse.  I am not familiar with them all.  One I am familiar with is gas core nuclear thermal rocket.  Some of the benchtop feasibility experiments were done 40 years ago.  But no test devices were ever built.  These are entirely "mythical" at this time,  but the projected performance looked good enough back then to make one-way trip times to Mars in the 30-90 day range possible,  all single-stage and completely re-usable.  But until and unless someone actually builds one,  these things remain speculations. 

GW

Well,  instead of a tow sack of surface dirt and rocks (Apollo),  why not add a real drill rig to the back of the rover.  Just about anybody can be trained to operate a drill rig.  Get your samples meters to a km down,  based on whatever you're seeing in the output cores.  Just like the oil drillers here.  Could do that pretty easily on Mars,  the moon,  or any other body with say 10% gee gravity. 

Drilling deep for samples.  Now there's a good reason to land men.  How do you program a robot to do that?  And with the time lag,  it's impractical to do it by remote control. 

Until that kind of thing is done,  you cannot answer fully the two questions:  "what all is there?",  and "where exactly is it?".  Until you answer them,  you have not really explored.

Isn't exploration supposed to be the purpose in going there?

GW

My congratulations to Spacex.  A feat very well done.  From one old rocket man to the entire Spacex team:  you are indeed "steely-eyed missile men" now,  for sure. 

Automatic launch abort,  quick repair,  launch,  all systems working, automatic flyby,  remote guided approach,  capture/dock,  and cargo delivery.  That's more than one "first" for the history books. 

All with a re-usable capsule that can carry astronauts.  There's more history that will be made. 

GW

I'd use a piece of well-proven ISRU equipment as part of my mission design,  as long as there was a back-up or "way out" designed into the mission.  You have to do that with everything,  anyway.  Once out of Earth orbit,  there is no practical possibility of rescue.  And I think we can all agree that there is nothing in this world as expensive as a dead crew.  Especially in government work. 

That being said,  what I see being discussed and referenced in the forums is beginning to convince me that effective and reliable ISRU for propellants might be something we actually can get "well-proven" in time to make the first trip.  Purity issues can be addressed,  yes,  but you have to find them first. 

Since the adsorption compressor principle we are talking about for Mars ISRU seems to be the same one as is in an oxygen system on the F-22 that is having problems,  well,  I think we just might have found one of the "gotchas".  If we get that fixed,  that's one less "gotcha" with the different hardware/same principle we'd use on Mars. 

It all gets down to doing the development phase correctly,  that much larger effort that goes in between the laboratory demonstrations and the actual application.  Development work is much more art than science.  None of the "gotchas" you are trying to find were ever seen before,  much less written about.  That's detailed,  frustrating,  dirty-fingernails work.  And there's a whopping lot of it to do,  before you ever consider your new product "well-proven". 

That's what the ISRU equipment needs to go through before we bet lives on it.  But it seems to me this could be done.  In time to go,  maybe even within the decade,  if need be.  That's just my experience-based hunch.  I do like what I'm reading about this stuff. 

GW

Rune - that's amazing.  I've never run numbers for a thing that large.  But I suspect the need for a shock absorber system "goes away" if the ship mass is large enough.  That actually helps.  Same ship would make a good colony-planting ship right here in the solar system,  too.  One whopping big transport.  Fast,  too.  That's cool. 

Everybody:

Isn't there some kind of "cryocooler" design floating around somewhere?  I keep hearing that word now and then.  Seems like a module with a solar electrolysis rig could be docked with another module (or modules) with solar powered cryocoolers.  Dock these with a bunch of water tanks,  and a couple of hydrogen and oxygen tanks.  Make water into LH2 and LOX slowly over time,  planning ahead to have the product tanks full at the time of need. 

I think this kind of thing would work for a fuel depot anywhere in the inner solar system where the sun is bright enough for solar power to work,  and also for a ship plying those same regions.  As long as your ship is modular,  that is.  You just need standardized modules for holding water,  LH2,  and LOX,  and for the two conversion equipment sets.  Standardize the design and hookup,  the same way we standardized shipping containers. 

Combine that with standardized engine and hab modules,  and a standardized docking interface for landers and crew return capsules,  and you have the "tinkertoys" to quickly and inexpensively go anywhere in the inner solar system with men.  Reuse the stuff,  re-tailor the stack-up for each mission.  Etc. 

As better engines become available,  you just fit them into that standard module envelope.  Chemical,  nuke,  doesn't matter.

The only trick is sizing the standardized modules.  Do that to support ships anywhere in the inner solar system,  not just Mars or an NEO.  Do it as reusable hardware,  so you launch the modules once,  then just resupply the water.  As money and interest becomes available,  use the same tinkertoys to go and do whatever is at hand. 

This is planning on 50 to 100 year timescales,  not just one-mission-at-a-time,  something the navies of the world have done (more or less) for multiple millenniums now.  Some do it better than others.  Technologies change,  but the approach is what matters.

GW

So,  let's go further than Mars.  Say,  to the asteroid belt.  Somewhere near 2 years one way,  something more like 6+ years round trip.  Don't you want to fly faster and cut that down?  Especially if you could refuel out there from frozen volatiles?  That engineering target ought to be a water-propellant gas core NTR.  Further,  depending on the solar cycle,  something like 2 to 4 years in space will incur a career limit radiation dose from galactic cosmic rays,  for which all known practical shielding techniques are rather ineffective.  Flying faster gets really important beyond Mars. 

When I looked at either gas core NTR or solid core NTR for Mars,  my vehicle accelerations were around .05 gee as I sized them.  That's a very few days burn for the very largest delta-vees,  orbit-to-orbit.  Electrics (and VASIMR is one),  have vehicle accelerations well under .001 gee,  which means you "burn" for much of half the trip there, just to accelerate,  and then you "burn" for much of the other half of the trip to decelerate.  Acceleration times over a very few days start incurring very significant solar gravity losses.  Fact of life. 

BTW,  the final NERVA testing had a rather radiation-free exhaust,  though few today believe (or want to believe) it.  They solved the core erosion problems,  and the daughter products stayed in the core.  900 Isp,  engine T/W about 3,6,  47 minute burn,  and multiple restarts is what they finally demonstrated.  And a large throttle ratio,  too.  In comparison,  there were major core mass losses in the early Phoebus and Kiwi series.  Very radioactive exhausts.  Some of that stuff is still out there on the nuclear test site in Nevada,  and will be dangerous for decades,  even centuries,  to come.  (Yes,  I do understand the dangers.)

Open-cycle gas core does have a radioactive exhaust,  but it's daughter products only,  not uranium or plutonium.  That's a different beast by orders of magnitude in terms of collateral radiation exposures.  (Myself,  I'd use thorium-bred U-233,  and avoid plutonium entirely,  but that's just me.)  The real advantage of open-cycle gas core is that it's an empty steel can when you shut it down.  Secondary-induced radioactivity in the engine structures decay in hours (at most) to safe levels.  No core on board to worry about when flying home,  or in a crash scenario.  The exhaust stream velocity generally exceeds solar system escape,  so if you don't point it at the ground,  you'll never pollute the atmosphere in the orbit-to-orbit application.  A truly abortable,  rather safe,  nuclear rocket.  Wow!  Is that ever at variance with widely-held public perceptions!

A lot of the fears being used even today to justify not doing nuclear propulsion,  are actually just completely irrational,  and at quite a variance with actual facts.  Not all,  but most of these fears.  There's real problems to design around,  of course,  but the advantages are simultaneous high thrust/high Isp,  especially when compared to every electric scheme I ever heard of. 

The only verifiably-doable thing I ever heard of in the last 50 years,  offering even higher thrust and Isp simultaneously than NTR,  is nuclear pulse propulsion. 

GW