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#1 2023-10-09 14:14:27

tahanson43206
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Registered: 2018-04-27
Posts: 16,473

Rocket Hopper for Mars Inter-City Travel

In a topic about trains on Mars, GW Johnson has offered a vision of rocket bus travel as the best solution for passenger travel on Mars.

This topic is available for all members to contribute to the business plan for this sensible sounding transport method.

(th)

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#2 2023-10-09 14:15:10

tahanson43206
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Registered: 2018-04-27
Posts: 16,473

Re: Rocket Hopper for Mars Inter-City Travel

GW Johnson wrote:

I still do not understand why so many propose such expensive and construction-effort-intensive notions for surface transport on Mars!  Few-to-none can afford high-speed trains or hyperloops or any of that stuff here.  With the transport costs to Mars so high,  what makes you think it will be affordable on Mars?  That's utter nonsense!

Sit down and think this through.  For most (essentially all) cargo,  speed is NOT of the essence.  It just needs to get there,  eventually.  Same as here.  We spend too much on highway truck transport here,  when we ought to be shipping more by rail.  The problem is that rail was an expensive and effort-intensive infrastructure on Earth,  and it will likely be worse on Mars,  due to the interplanetary transport costs and the lethally-harsh conditions on Mars.

So,  what you want is surface transport with the characteristics of rail transport,  but not the high infrastructure-emplacement costs of rail as we know it here.  I briefly described such,  in post 252 above.

Creating a graded dirt road is easy,  way-easier than laying track.  On Mars,  you need not worry about rainwater drainage,  so the graded spoil embankments can remain alongside your smoothed surface.  We don't get to take that cheap approach on Earth,  but we can on Mars!  All you need is a big,  powerful road grader,  which can be a big tractor vehicle rather similar to the large ore carriers used in mining here.  The Martian one will need to be electric.  It can run on power from a small reactor,  either on a small trailer behind,  or via an extension cord from a stationary reactor.  Just mount a big blade on the thing,  and get to work!

Once the road is built,  take the blade off the tractor.  Take the driver out of the tractor,  and put self-driving software in charge.  This thing is quite powerful,  or it could not have graded the road.  Let it pull a whole string of trailers behind,  carrying cargo.  This is the basic freight train idea,  but without any tracks!  The software simply steers it between the spoil embankments,  until it reaches destination.  Put solar panels atop all the train cars,  and power the electric tractor that way.  Just move slow,  so the power demand is not too high for solar.   So what if it only moves in daylight?  Who cares?  So what if it only moves at walking speed?  Who cares?

Moving people point-to-point is different.  Time is an important consideration.  They need to fly,  somehow.

Lighter-than-air won't work,  whether done by hot-air methods,  or lifting-gas methods.  The density differences are so low at Martian atmosphere densities,  that the lift force you get will always be less than the Mars weight of any practical gas bag material.  Even in Hellas Basin:  twice next-to-nothing is still next-to-nothing.

Winged airplanes won't work,  because the densities are so low,  that despite 38% gee,  your landing speeds look like airliner cruise speeds here.  That will never work,  because the risk of a high-speed accident is so high that close to the surface,  during both takeoffs and landings. 

Helicopters scaled-up to carry people likely will not work on Mars,  because of low density effects far outweighing lower-gravity effects.  There is a square-cube law that limits what any aircraft (helicopter or fixed-wing) can do,  because materials are only so strong.  At small size,  drones can do things we have never been able to do with full-size helicopters here on Earth.  The situation is even worse on Mars.  Weight is reduced by factor near 3,  yes,  but density (and therefore aerodynamic forces,  is reduced by a factor of over 100. That utterly overwhelms you,  except in the very smallest sizes (Ingenuity is the tiny example,  and it just barely flies with no payload at all).

That leaves suborbital rocket travel.  At suborbital speeds,  there is not very much aerobraking available at journey's end,  so the landing dV will be comparable to the launch dV,  but I bet even their sum is less than the dV to low orbit,  even for a journey nearly halfway around the planet.  And little or no heat shield is required on Mars.  At least it is something to look closely at!  Plus,  here is a second reason to build propellant-manufacturing infrastructure on Mars.

GW

(th)

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#3 2023-10-12 16:18:31

GW Johnson
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From: McGregor, Texas USA
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Posts: 5,385
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Re: Rocket Hopper for Mars Inter-City Travel

I'm working on the rocket hopper idea.  Nothing to report yet,  except that this is way more difficult than I initially thought. 

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#4 2023-10-15 16:09:00

GW Johnson
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From: McGregor, Texas USA
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Posts: 5,385
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Re: Rocket Hopper for Mars Inter-City Travel

I got one!  It would seem capable up to about 9500 km range,  which is almost antipodal (10,637 km). 

28 metric tons at launch,  10 souls aboard.  It has about 20 tons max propellant load.  Load less for shorter ranges.

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#5 2023-10-15 19:06:20

SpaceNut
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#6 2023-10-15 19:08:56

tahanson43206
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Registered: 2018-04-27
Posts: 16,473

Re: Rocket Hopper for Mars Inter-City Travel

For SpaceNut re #5

Thanks for logging in and for adding content to the new topic !!! GW Johnson has completed a study showing a practical solution for a rocket to carry 10 people around the planet using methane and LOX.  The paper and slide show are finished and I'll try to get them posted in the next few days!

(th)

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#7 2023-10-15 19:57:46

kbd512
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Re: Rocket Hopper for Mars Inter-City Travel

Wikipedia - New Shepard Suborbital rocket

The launch vehicle is designed to be fully reusable, with the capsule returning to Earth via three parachutes and a solid rocket motor. The booster lands vertically on the same launchpad it took off from. The company has successfully launched and landed the New Shepard launch vehicle 22 times with 1 partial failure deemed successful and 1 failure. The launch vehicle has a length of 15.0 m, a diameter of 3.7 m and a launch mass of 75 T. The BE-3PM engine produces 490 kN of thrust at liftoff.

New Shepard is powered by LOX/LCH4, it has 110,000lbf (GW's concept used a trio of 30,000lbf engines), and I presume the capsule can seat more people.  This vehicle has a crew / capsule escape system as well.

Inconel 625 has a maximum service temperature of 1,800F.  GW stated that the windward side would be heated up to 1,950F, which means a thin layer of heat shielding material would need to protect the exterior of the vehicle.

PICA-X has been tested to 3,500F, but SpaceX uses the improved PICA-3 now.

LI-900 tiles (9lbs/ft^3) from STS are suitable for service to 2,200F.  LI-2200 tiles (22lbs/ft^3) is suitable for high aerodynamic stress areas like landing gear doors.

TUFROC insulation is very similar to the Space Shuttle tile and RCC, but with improved reusability temperature capability, as well as being mechanically tougher than traditional STS tiles and RCC, meaning able to survive rain in Earth's atmosphere during ascent, without destruction, and presumably a peppering of dust particles on Mars.

NASA TUFROC Reusable Insulation

Toughened Unipiece Fibrous Reinforced Oxidation-resistant Composite (TUFROC) is a tiled Thermal Protection System (TPS) suitable for reusable entry heating at 2900°F and with single use potential up to at least 3600°F

TUFROC was initially developed for NASA’s X-37 project and ultimately resulted in use on the Air Force X-37B as the wing leading edge (WLE) of the vehicle

TUFROC has similar high temperature capability compared with carbon/carbon, but is manufactured at an order of magnitude lower cost & faster schedule

TUFROC System Design

1. The ROCCI cap consists of a carbon fiber preform with a silicon oxycarbide (SiOC) matrix for oxidation resistance
2. ROCCI receives surface treatments to control thermal-expansion followed by a Reaction Cured Glass (RCG) coating to control emissivity and reduce oxygen diffusion into ROCCI
3. The ROCCI cap is mechanically and adhesively attached to a silica tile base, typically Alumina Enhanced Thermal Barrier (AETB)
4. AETB provides enhanced insulative performance
5. The resulting system looks and behaves like a black Shuttle tile with increased temperature capability

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#8 2023-10-16 13:25:48

tahanson43206
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Posts: 16,473

Re: Rocket Hopper for Mars Inter-City Travel

This post is reserved for a set of links to files GW Johnson has prepared for presentation.

The theme is his design for a 10 passenger rocket powered transport vehicle for Mars.

The design takes the thin atmosphere of Mars into account.

Of interest to those who remember Dr. Zubrin's methane/LOX design, this vehicle also uses methane/LOX

SearchTerm:Hopper Rocket Hopper for Mars - design by GW Johnson October 2023

1) https://www.dropbox.com/scl/fi/5grix44h … 13918&dl=0

PDF version of #2) https://www.dropbox.com/scl/fi/qnc16c37 … 3fnvz&dl=0

2) https://www.dropbox.com/scl/fi/wrtde2xw … 7wd9s&dl=0

3) https://www.dropbox.com/scl/fi/hl25a4pk … 5ll6j&dl=0

PDF version of #4) https://www.dropbox.com/scl/fi/gl9b44ye … 9vfcp&dl=0

4) https://www.dropbox.com/scl/fi/ftfajkb7 … vtugz&dl=0

Following is text provided by Dr. Johnson to supplement the links above:

“Rocket Hopper for Mars Inter-City Travel” thread:

What I created for the “Mars rocket hopper” was two presentations,  one longer,  the other shorter.  Both exist as Powerpoint slide sets,  and as pdf documents with explanatory text and the same images as are in the corresponding slides. 

The longer presentation exists as a 12-slide set and an 8-page document.  There are 9 slides and images with real “meat” on them that give the data and characteristics of the final design concept I came up with.  It is a single stage reusable rocket vehicle that uses propellants thought to be manufacturable on Mars,  with engines that do not push the state of the art.

None of this includes all the multiple iterations I went through and the multiple mistakes I made,  getting to a configuration that actually seems feasible.  But I did manage to get around the Mars entry/descent/landing (EDL) dilemma with something grossing 28 metric tons at launch,  and almost 9 tons at entry! 

It’s not a general EDL solution,  it’s restricted to this specific vehicle and application,  with a max entry speed of only about 3.5 km/s,  and a shallow entry angle.  Even so,  direct and immediate rocket braking is how the landing must be made.  It flies almost halfway around the planet,  suborbitally.

The shorter presentation exists as a 6-slide set and a 3-page document.  There are 4 slides with “meat” on them.  This is more of just a teaser,  since a lot of the supporting characteristics and data are missing.

Tahanson43206 has posted 4 links here.  The first is to the short “teaser” document,  the second is to the longer slide set,  the third is to the longer document,  and the 4th is to the short “teaser” slide set.

I would recommend the two documents for people wanting to understand what I did.  The slide sets are really for already-knowledgeable persons presenting these things to others.   

Please understand that the “rocket hopper” is for the fast transport of low masses of time-sensitive stuff,  mostly people,  but also small perishable items like packages of medicines.  Bulk freight goes slowly on the surface,  being time-insensitive.  I looked at that,  too.  That’s in the “Trains on Mars:  Could a rail system provide Martian need” thread.


“Trains on Mars:  Could a rail system provide Martian need” thread:

I looked at how to effectively provide a freight train on Mars,  but without having to build any tracks.  Emplacing infrastructure is effort-intensive and costly on Earth;  it will be far worse on Mars because of the transportation difficulties just getting there. Plus the conditions are harsher and quite lethal to human workers.

What I came up with was a “truck train”:  a tractor vehicle pulling freight wagons,  all rolling on a simple graded dirt road on tires (which may need a bit of heating to prevent cracking in the cold.  The thing is quite slow,  but bulk freight is very time-insensitive,  just like here on Earth. 

It must be rather slow in order not to over-tax the solar panels on the roofs of the freight wagons that provide the electricity to power the tractor.  It is also self-driving,  but with manned operation capability should the need arise.  The same tractor fitted with a big blade is what grades the road in the first place.  But,  that is inherently a manned operation,  just like dirt work here on Earth.  For that,  a shielded trailer containing a small nuclear power generator must power the tractor. 

What Tahanson43206 has posted is two links to two forms of the 11-slide Powerpoint presentation I created.  8 of these slides have real “meat” on them.  The first link is to the original Powerpoint form of the slides,  and the second link is to the pdf form of those same slides.  I now have a pdf document with explanatory text and those same images,  which is the better thing to learn from.  I hope to get him to post a third link here,  to that document.

This is the best solution that I could come up with,  for transport of time-insensitive bulk freight on Mars.  It has no infrastructure to emplace other than grading and preparing the dirt road,  which is a very minimal investment to make.  Most of the other concepts I see discussed require massive supporting infrastructure,  and usually involve materials and construction processes not yet adapted to Mars.  Everything we need for the “truck train” idea already exist in forms we can easily use on Mars,  and there is little infrastructure,  making the costs far more feasible.

Time-sensitive items would be small packages,  perhaps medicines,  and people.  Fast trips require flight,  most forms of which won’t work on Mars at a scale large enough to carry people.  My best take on that is posted as a “Mars rocket hopper” over in the “Rocket Hopper for Mars Inter-City Travel” thread.

(th)

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#9 2023-10-16 15:20:56

tahanson43206
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Registered: 2018-04-27
Posts: 16,473

Re: Rocket Hopper for Mars Inter-City Travel

For all members ... please help to make Post #8 as inviting as possible for non-member forum readers.

The plan is to invite folks outside the immediate membership to view the materials on offer in Post #8.

I'll ask Dr. Johnson for text to go with each link, but we would appreciate any suggestions from members who might have suggestions.

For that matter, the material is sure to stimulate questions, which (I'm sure) GW will be happy to attempt to answer.

In the Sunday Zoom, when GW went through a first rehearsal for the upcoming NSS presentation, he got a number of questions from his audience.

PS... there is a ** lot ** of detailed calculation behind the presentation.  If there is someone who ** really ** wants to know how the numbers were derived, please ask.

(th)

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#10 2023-10-18 17:39:59

SpaceNut
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Posts: 28,639

Re: Rocket Hopper for Mars Inter-City Travel

Treat the rocket the same as space x falcon and leave 1/4 of the fuel load for landing from a near orbital parabolic flight for a single stage and we can use even other fuel types.

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#11 2023-10-19 10:17:37

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,385
Website

Re: Rocket Hopper for Mars Inter-City Travel

I was using a vacuum CF = 1.837239 for the nozzle,  expanding from 2000 psia to 5.97 psia,  so that the engine could be tested at sea level and 67+% power without separating.  This includes the effects of nozzle kinetic energy efficiency for an 18-8 degree curved bell.

Shortcut calculation listed in some textbooks for Isp is Isp = CF c* / gc,  but that ignores the effects of nozzle throat discharge efficiency CD,  and (more importantly) the effects of the cycle bleed gas dumped fraction BF.  The corrected equation reads:  Isp = CF c* (1 – BF)/CD gc.  Usually,  for a well-designed nozzle profile,  CD will be near 0.995.  But only for a full-flow cycle will BF be zero. I used BF = 0 in my modelling.  Every percent of BF that is not zero is a percent “right off the top” from Isp!

The chamber characteristic velocity c* is a measure of the propellant combination performance that is independent of nozzle performance.  It varies slightly with chamber pressure level as a power function of pressure,  but that exponent is rather low (near 0.01) so the effect is not a strong one.  Here are some data at 1000 psia Pc for a few propellant combinations:

O2 – H2:           7950 ft/sec
O2 – CH4:         6120 ft/sec
O2 – RP-1:        5900 ft/sec
O2 – NH3:        5880 ft/sec  (used in the X-15’s XLR-99 engine)
(100%)H2O2 – N2H4:  5770 ft/sec (pure peroxide with plain hydrazine)
N2O4 – N2H4:  5860 ft/sec  (plain hydrazine)
N2O4 – CN2H6: 5730 ft/sec) (monomethyl hydrazine)
N2O4 – UDMH: 5680 ft/sec (unsymmetrical dimethyl hydrazine)
N2O4 – Aerozine50:  5560 ft/sec (50-50 blend of plain hydrazine and UDMH)

Not correcting for the higher chamber pressure is crudely only a 0.7% error.  So,  using the c* data as they are in the corrected Isp shortcut,  with CD = 0.995 and BF = 0,  at vacuum CF = 1.837239,  you get the Isp’s here:

O2 – H2:             456.25 sec    Vex = 4.474 km/s
O2 – CH4:           351.2 sec      Vex = 3.444 km/s
O2 – RP-1:          338.6 sec      Vex = 3.3205 km/s
O2 – NH3:          337.5 sec      Vex = 3.310 km/s
H2O2-N2H4:      331.1 sec     Vex = 3.247 km/s
N2O4 – N2H4:   336.3 sec     Vex = 3.298 km/s
N2O4 – CN2H6: 328.8 sec     Vex = 3.224 km/s
N2O4 – UDMH: 326.0 sec     Vex = 3.197 km/s
N2O4 – Aerozine50:  319.1 sec   Vex = 3.129 km/s

If we assume we need to reach 3.6 km/s speed as delivered post launch on Mars,  then factor that up about 2% for gravity and drag losses.  That would be 3.672 km/s.  Now add a budget for midcourse corrections of0.2 km/s,  and a budget for the post-serobraking direct rocket-thrust landing,  assuming altitude is too low to use any sorts of chutes.  The local Mach 3 speed to kill is 0.7 km/s,  and you must dramatically factor that up to cover losses,  and the need to hover and diver around rough-field obstacles. 

I would never use less than factor of 1.5 for that,  and would prefer 2.  Using 2,  the landing dV is 1.4 km/s.  The mission total is 3.762 + .2 + 1.4 = 5.272 km/s. 

The effective exhaust velocity is the Isp * gc,  which in metric units is (Isp, s) * (9.80667 m/s2)/(1000 mps/kps) to get km/s.  I already put that in the table above.

Solving the rocket equation “in reverse” to get mass ratio MR from the dV and Vex data;  the equation is MR = exp(dV/Vex).  That number is as follows,  for each propellant combination.  The corresponding propellant mass fraction fprop = Wp/Wign = 1 – 1/MR.  Propellant + inert + payload must sum to ignition,  so fpay = 1 – fprop – finert. 

I used finert = Winert/Wign = 0.14 in my vehicle modelling.  One can always argue about it,  but that value is quite optimistically low (!!!) for a vehicle that is reusable,  has rough-field,  wide-stance landing legs that fold up,  and likely must have at least a little bit of heat protection near the stagnation zone for entry.  Using that same value finert = 0.14 here,  the payload fractions fpay are also given.  If negative,  the mission is beyond the capacity of that propellant combination,  when used with the nozzle modelled here.  As it turns out,  these are all positive.

O2 – H2:  MR = 3.249  fprop = 0.6922   fpay = 0.1678
O2 – CH4:  MR = 4.622   fprop = 0.7836  fpay = 0.0764
O2 – RP-1:  MR = 4.893  fprop = 0.7956  fpay = 0.0644
O2 – NH3:  MR = 4.917  fprop = 0.7966  fpay = 0.0634
H2O2-N2H4:  MR = 5.072  fprop = 0.8028  fpay = 0.0572
N2O4 – N2H4:  MR = 4.946  fprop = 0.7978  fpay = 0.0622
N2O4 – CN2H6:  MR = 5.131  fprop = 0.8051  fpay = 0.0549
N2O4 – UDMH:  MR = 5.202  fprop = 0.8078  fpay = 0.0522
N2O4 – Aerozine50:  MR = 5.392  fprop = 0.8145  fpay = 0.0455

So,  as it turns out,  all these propellant combinations might be technologically useful,  although many have payload fractions near only 5%.  But of all these,  present thinking says only methane and hydrogen,  along with oxygen,  can be made on Mars! 

The methane-oxygen will carry not quite 8% payload fraction on this mission,  and the hydrogen-oxygen a bit over 16% payload.  These are the smallest,  lightest ship designs for the rocket hopper.  Bear in mind that the bigger and heavier the hopper is,  the bigger will be its ballistic coefficient,  and the harder it will be with the aerobraking design,  in order not to smack the surface while still hypersonic. 

I had severe troubles getting a workable entry/descent/landing design with the methane.  Low entry angle proved to be essential,  and that greatly impacts what suborbital trajectory you can use!  Hydrogen would be somewhat easier,  because all the masses (including mass at entry) are smaller.  Nuclear thermal would be very difficult indeed for entry/descent/landing on Mars,  because of the heavy reactor core,  despite the higher Isp.

Them’s just the numbers,  guys!  Everybody has to live within these bounds on Mars!

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#12 2023-10-19 10:47:39

Void
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Registered: 2011-12-29
Posts: 6,860

Re: Rocket Hopper for Mars Inter-City Travel

Dr. GW Johnson, Thank you.  I have captured your post into a reference of mine along with other thing previously there: http://newmars.com/forums/viewtopic.php … 13#p190313

Moderators, I think you might consider a place to put references to exceptional posts, in a manner similar to what I have done.  Perhaps only for moderators to edit.

Done

Last edited by Void (2023-10-19 10:50:07)


Done.

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#13 2023-11-05 12:05:07

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,385
Website

Re: Rocket Hopper for Mars Inter-City Travel

I finished my methane-oxygen rocket hopper study.  I posted the results over at my "exrocketman" site as "Rocket Hopper for Mars Planetary Transportation",  posted 1 Nov 2023. 

The questions considered at the outset of that study also led me to the truck train concept for surface bulk freight shipment on Mars.  I finished that as well,  and posted it on "exrocketman" as "Surface Freight Transport on Mars",  posted 4 November 2023. 

With only minimal design changes,  the rocket hopper could also double as a minimalist orbital taxi on Mars. That's still left to investigate.

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#14 2023-11-05 13:08:06

tahanson43206
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Posts: 16,473

Re: Rocket Hopper for Mars Inter-City Travel

For those who might wish to hear a summary presentation by GW, he will be rehearsing this evening in the Zoom meeting. At this point, we have one NSS chapter member planning to attend, to audit the presentation.  There are details to be worked out to turn this into a video that can be served (via YouTube) from our web site and theirs.  If this initiative is successful, GW has a ** lot ** of other presentations to offer.

As a reminder, we are using Zoom, so if you'd like to attend, please install Zoom on your system (Windows, Linux or Apple), and ** please ** test the link to the Waiting room at the top of Post #1 of the Zoom topic.

We will be monitoring the Zoom topic for inquiries during the meeting.

(th)

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#15 2023-11-13 09:31:28

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,385
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Re: Rocket Hopper for Mars Inter-City Travel

It is beginning to look like what I sized for a suborbital Mars rocket hopper capable of reaching almost halfway around the planet,  could also serve as a low-orbit taxi,  including rendezvous chase to match-up orbital positioning with some in low circular orbit.

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#17 2023-11-13 20:03:25

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 28,639

Re: Rocket Hopper for Mars Inter-City Travel

Still looking for an engine to make use of as we appear to not have one.

We also must remember that the liquid is still put to a pressure an if i recall the Lox tank of the shuttle was 20 PSI.

Mars Rocket Propulsion System

Propellant performance of Mars-produced carbon monoxide

Mars In-Situ Resource Utilization Based on the Reverse Water Gas Shift: Experiments and Mission Applications

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#18 2023-11-13 20:28:15

tahanson43206
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Posts: 16,473

Re: Rocket Hopper for Mars Inter-City Travel

For SpaceNut ... have you read the papers that GW Johnson has published?

If I understand the work correctly, he has designed engines from scratch for this application.

He chose CH4 and LOX as the propellant.

The reasons are given in the presentations.

(th)

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#19 2023-11-14 19:16:51

SpaceNut
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Posts: 28,639

Re: Rocket Hopper for Mars Inter-City Travel

Just now getting to the page for GW's information

https://exrocketman.blogspot.com/2023/1 … etary.html

you are correct that if we reuse the Raptors of the cargo ships it will satisfy the design with these fuels.

engine burns liquid methane fuel with liquid oxygen oxidizer,  similar to SpaceX’s Raptor and Blue Origin’s BE-4.

The raptor is well known but the BE-4 is yet to show how it will perform.

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#20 2023-11-15 10:43:59

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,385
Website

Re: Rocket Hopper for Mars Inter-City Travel

Raptors out of a Starship on Mars could be put into something else,  that is true.  It would need to be a big "something else",  because a Raptor's thrust level ins in the 200-250 metric ton-force range,  depending on which version. 

What I was looking at for the "rocket hopper" was a cluster of 4 small "paper" engines,  each 30,000 lb = 13.6 metric tons-force.  I was using 4 to get both engine-out reliability and safety,  plus a larger effective throttle-down range when most of the propellant is burned off.  Even if we went to single-engine,  the thrust would be 120,000 lb = 54.4 metric ton-force,  and it would need deep throttle-down capability (to around 8-10 metric ton-force (that's over 5:1 throttle-down,  not even Raptor does that).

My "rocket hopper" carrying only 10 people in pressure suits,  would have to be very much larger to use Raptor engines.

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#21 2023-11-15 11:42:20

tahanson43206
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Registered: 2018-04-27
Posts: 16,473

Re: Rocket Hopper for Mars Inter-City Travel

For GW Johnson re #20

The competing rocket companies are making smaller engines that burn methane and LOX.  Perhaps one of their existing designs might work for your application. You are going to need partners with deep pockets and a long range vision.  Perhaps that is where we might look.

Please start the process by looking over the small engines in development and use by the smaller rocket companies.  In particular, I am thinking of the one that makes it's engines using 3D Printing.  Assuming that claim is accurate, it would imply an easier manufacturing process at Mars, where there is no infrastructure.

You're going to be going through engines when folks start arriving at Mars, so you'll need more than just an initial set.

One factor that does concern me about the business of flying customers at Mars is the greater risk factor compared to Earth.  There isn't enough air to support parachutes for safety, so those engines and all the plumbing need to be extremely reliable.

(th)

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#22 2023-11-15 13:03:47

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 3,285

Re: Rocket Hopper for Mars Inter-City Travel

Maybe a pressure fed engine, with a lining instead of regenerative cooling, burning a hypergolic or easily ignitable propellant.  Maybe methanol and hydrogen peroxide?  The H2O2 can be decomposed by passing it over a hot platinum catalyst, producing hot oxygen and steam which then react with the methanol.


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#23 2023-11-15 18:25:39

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 28,639

Re: Rocket Hopper for Mars Inter-City Travel

most of the engines are currently for thrusting and are not all that large.

http://www.astronautix.com/l/loxlch4.html

So unless we are designing a non space x mars lander that is much smaller in size then we are sending the engines to make use of with the salvaged parts of a cargo ship.

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#24 2023-11-17 11:28:18

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,385
Website

Re: Rocket Hopper for Mars Inter-City Travel

When doing a mission feasibility study,  one is not very concerned with trying to use pre-existing engines,  one is far more concerned with what the engines and the other components should really be,  in order to accomplish the proposed mission. 

If the needed engine characteristics match an existing or modifiable device,  fine.  But if not,  it still gives you guidance as to what new designs might be needed.  The idea is to bound the problem,  not to finally solve it.  But either way,  the result is illuminating,  while still light years away from a final detailed design. 

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#25 2023-11-19 10:23:31

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,385
Website

Re: Rocket Hopper for Mars Inter-City Travel

I was able to resize the geometry and mass fractions a little,  and came up with a vehicle about 38 metric tons at launch,  if fully loaded with propellants and payload.  It could carry 10 people in p-suits with supplies and luggage to low Mars orbit at low inclination eastward.  That would include a parking orbit "chase" to synchronize with something already in the orbit,  plus rendezvous-and-dock,  deorbit,  and a landing burn for direct rocket braking. 

The same vehicle fully loaded could take the same payload nearly halfway around the planet,  using a suborbital trajectory that exited and re-entered the atmosphere at roughly the same speed as going to orbit,  but at a steeper angle.  Entry descent and landing is more challenging by far on the suborbital trajectory,  because of the steeper entry angle.  Surprisingly,  this trajectory needs a bit of heat shielding in the stagnation zone,  when the orbital entry does not. 

Shorter suborbital ranges obtain by loading less propellants,  but using the same payload and inert.  I looked at ranges down to just under 500 km. You have to be careful to load the correct amount of propellant for the mission,  so that you are not too heavy at entry. 

Launch gee starts at just under 1.5,  and ends up in the neighborhood of 4.  I got entry gees down to 4.5 worst case,  nearer 2 for most of the missions.  Landing burn gees is also near 2.5 gees.  The solution space was quite narrow for the suborbital flights,  all those end-of-hypersonics altitudes were 7-8 km from the surface.  The orbital entry ended its hypersonics up nearer 20 km,  because of the much shallower entry angle. 

Those descriptions belie how many false starts and iterations I had to go through to come up with this.  But my results clearly show there is a solution space for a Mars rocket hopper that is also a Mars orbital taxi,  and what ballpark that solution lies in.  That project is now ready for "someone else" to apply real computer-aided design processes to.  I did this with simple hand calculations,  assisted by a spreadsheet for easy iterations,  but essentially the same analysis as was done in the slide rule days.

All of this,  and the surface transport "truck train" idea,  came from two fundamental considerations for travel about Mars:  (1) time-sensitive stuff like people needs to fly,  while time-insensitive stuff like bulk freight needs to go slowly on the surface,  and (2) you want to emplace the very minimum infrastructure in order to make travel possible,  which costs a lot to emplace here,  and "astronomically" more to emplace on Mars. 

I could not see a way to make airplanes,  helicopters,  or lighter-than-air work in the thin atmosphere of Mars at a scale big enough to carry people.  But I could make suborbital rocket travel work,  presuming propellants can be made in situ and in mass quantities on Mars.  Similarly,  the bulk freight needed a train,  but one without all the tracks to build.  So it became a "truck train" on a graded dirt road.

GW

Last edited by GW Johnson (2023-11-19 10:24:20)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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