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#1526 2021-10-26 14:07:47

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,087

Re: Starship is Go...

An interesting presentation.

Not least, the suggestion that a Starship will be able to carry 175 tons of cargo - I have assumed 100 tons max before now.

He doesn't explain what the "average" insolation means. Average for the whole planet or for areas of maximum insolation?

I think the mass estimate for a solar solution is too high, because with such clement conditions on Mars (low force winds and no precipitation to speak of) we don't need the robust scaffolding required on Earth. In fact, it might be simpler to take more solar panelling and simply lay it out on the ground or rest it on wires strung between lightweight poles, or on inflatable supports. Whatever, I suspect you can probably reduce the mass estimate by at least 30%.  13,000 sq metres sounds like a lot but it's only 114 x 114 metres.

The suggestion that we would need to rely on dirty ice is not persuasive. NASA/JPL have identified 97%-plus pure ice a few feet below the surface in the Erebus mountains region. And that is a good area to land and start a first base (as recommended by JPL).

Discovering that your ice source is going to be further away than expected is not going to be a huge tragedy as long as you have enough transporter rovers to keep up a good supply chain. We might need maybe 4 x 2 ton robot rovers to transport ice back to the base. You would have to work to a "worst case scenario" - so maybe working anywhere up to 50 kms away from the base.

I think his idea for dispensing with the need for propellant production on Mission One is very interesting and should be investigated further.

A lot of things become possible if each Starship can take 175 tonnes to Mars. For one thing, a couple of Starships could carry the methane (220 tonnes) for a Starship return journey. You would then only need to produce as ISRU 780 tonnes of oxygen on the surface of Mars. But electrolysis is a pretty simple process as I understand it and can easily be scaled up. We could then just vent the hydrogen or use it as a power reserve.

This would reduce the mass required for the solar power solution and for CO2 concentration.

I'm beggining to think that might be the best way forward, applying the "KISS" principle.

Oldfart1939 wrote:

Here's an excellent presentation by Marcus House on a method of doing an Earth Return w/o ISRU; there are lots of numbers involved and talk about Isp, electricity needed on Mars , and kinda shoots down the exclusively Solar power production using very nicely calculated information. The guy really talks fast so be prepared to watch several times ad stopping to look at the tables he presents.

https://www.youtube.com/watch?v=u55zpE4r-_Y


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#1527 2021-10-26 18:33:00

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 23,851

Re: Starship is Go...

Louis any increase is due to performance increases in engines and dry mass reduction. The other thing that makes the final change is the transit time which will get longer as the payload mass increases. Dam that math stuff....

Δv - Desired Change In Rocket's Velocity
vₑ - Effective Exhaust Velocity
m₀ - Initial Mass (Rocket Plus Contents Plus Propellant)
m₁ - Final Mass (Rocket Plus Contents)
Δv = vₑ ln(m₀ / m₁)

Here is the reference system for fuel manufacturing
https://marspedia.org/images/thumb/a/a2 … uction.png

Its says 13,000 kwhr a day with the 100w m^2 panels getting 10 hrs each day or creating 1 kwhrs.

Mars does not receive 10 hours of sunlight at full power for that to work.

With no battery mass stated...

There is no mass for the co2 collection and processing and there is none given for the water gathering let alone that mass for melting and cleaning the water....

It also will take 6 of these units to get the fuel delivery in a 500 day not 678 day mars cycle to refill a single starship for return home.

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#1528 2021-10-27 14:46:58

louis
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From: UK
Registered: 2008-03-24
Posts: 7,087

Re: Starship is Go...

I may be missing something re the journey time but surely the increase from 100 to 175 tons cargo must be coming from a reduction of some 75 tons in the weight of engines, fuel/propellant and dry mass? Is that not the case?  If it is, then the journey time should presumably remain the same I am presuming, as the overall mass remains the same.

There doesn't need to be a huge battery mass required if you are making hydrogen (or methane) and oxygen - burn the hydrogen to power a steam generator (well you'd actually take several).  But there will already be large battery installations on each Starship.

Yes, I don't know who's right about solar power at the surface. It is certainly the case that on Mars because of the dust content in the atmosphere, the light is much more diffuse and so, while the mid-sol maximum may be less than the earth equivalent as a % of total solar power during the sol, at either end of the sol, solar power is stronger than would otherwise be the case, as the light is bouncing in all directions. I also understand the Mars wobble means that solar power is more evenly distributed over the year.

SpaceNut wrote:

Louis any increase is due to performance increases in engines and dry mass reduction. The other thing that makes the final change is the transit time which will get longer as the payload mass increases. Dam that math stuff....

Δv - Desired Change In Rocket's Velocity
vₑ - Effective Exhaust Velocity
m₀ - Initial Mass (Rocket Plus Contents Plus Propellant)
m₁ - Final Mass (Rocket Plus Contents)
Δv = vₑ ln(m₀ / m₁)

Here is the reference system for fuel manufacturing
https://marspedia.org/images/thumb/a/a2 … uction.png

Its says 13,000 kwhr a day with the 100w m^2 panels getting 10 hrs each day or creating 1 kwhrs.

Mars does not receive 10 hours of sunlight at full power for that to work.

With no battery mass stated...

There is no mass for the co2 collection and processing and there is none given for the water gathering let alone that mass for melting and cleaning the water....

It also will take 6 of these units to get the fuel delivery in a 500 day not 678 day mars cycle to refill a single starship for return home.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#1529 2021-10-28 11:53:06

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,690
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Re: Starship is Go...

Louis,  while you are right about the effects of inert mass,  it's more complicated than you think.  A lot more.

The payload Starship can carry to Mars from LEO varies with the refill level in LEO,  with the trajectory selected for transit to Mars,  and with the inert mass fraction of the vehicle.  The numbers I have for this are my best-guess reverse engineering estimates,  based on mostly hearsay for vehicle inert mass.  They indicate that maybe 150 tons payload per vehicle is feasible for trajectories 6 to 8.5 months long,  with only a partial refill in LEO by 4 or 5 tankers. 

Min energy Hohmann with a full refill (9+ tankers) is over 300 tons payload by the assumptions I made,  but that is the 8.5 month trajectory on average,  and an unaffordable (and possibly technologically-impossible) number of tanker flights and on-orbit propellant transfers.  And note that no such cryogenic transfer from ship to ship has ever yet been done.  Not by anyone.  Not yet. 

Launch to LEO is quite different,  and the payload capability is also different (it is less).  For one thing,  there are two completely different vehicles flying two completely different trajectories.  Those vehicles are Starship-to-LEO and Superheavy-reverse-back-to-launch-site.  That's two different inert mass fractions.  And the gross mass of the Starship is precisely the payload Superheavy must carry,  but only over the first part of its trajectory,  away from the launch site. By the time I balanced all that out,  and got Superheavy credibly back to launch site for a powered landing,  the max possible payload Starship could reach orbit with was 140-150 tons.

Again these are reverse-engineering estimates,  some of which (the inert mass fractions (plural) are based on hearsay.  I am not privy to the actual numbers that the SpaceX engineers use,  nor do I have a real trajectory code,  or the aerodynamics data using it would require.  These are rocket equation estimates,  with judicious "jigger factors" for gravity and drag losses,  based on past experiences doing this for a living with the various missiles,  and the old "Scout" satellite launcher.

I couldn't be that bad at it,  because my estimates are falling right in the ballpark with what has actually been achieved so far.

Now you might say send two 150 ton payloads to LEO,  and combine them aboard one ship to make a 300 ton payload sent to Mars from LEO with a full 1200 ton refill. Except that you think moving 1200 tons of propellant ship-to-ship through plumbing connections is hard,  try moving tons at a time in zero gee of solid cargo.  Not even SpaceX has ever proposed a thing like that!  Not even in Musk's wildest tweets!  And for good reason.

Beyond that,  don't forget that the approach Spacex is gunning-for is to catch the Superheavy and the orbital Starship so as to reduce their inert mass fractions by leaving off the landing legs,  saving multiple tons of inert mass.  Whether that will really work is more-than-debatable,  and even SpaceX acknowledges that they cannot do that going to the moon or Mars.  Some sort of landing legs are simply required.  And you have already seen what I think of the "6-legs" they were using in the earlier Starship suborbital tests. Those WILL NOT work on the moon or Mars. 

Even if that crazy rocket-catching scheme can be made to work,  what happens if (really WHEN) you must make an emergency landing off-site?  A dead crew from a bad management decision is THE MOST EXPENSIVE mistake anyone can make!

Whether Starship can get to orbit with 150 or 175 tons is ALMOST IRRELEVANT now.  Why?  Because the thing is still a highly experimental vehicle.  Even once they start flying stuff to orbit,  that kind of Starship won't be the same as the kind required to go to the moon,  in turn quite different from the one required to go to Mars.  No one,  not even SpaceX,  knows what those designs will really be.

That kind of unpredictable change is just the nature of flight test and engineering development work.  But,  it means when you start splitting hairs over what you could do with 175 tons to Mars vs 150 tons,  you really are just arguing angels on the head of a pin.  It's quite the pointless speculation.  Which is exactly why the SpaceX website does not promise payload numbers to Mars yet,  nor even to LEO,  except to say "over 100 tons".  Go read it for yourself.

GW

Last edited by GW Johnson (2021-10-28 12:05:08)


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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#1530 2021-10-28 12:54:36

RobertDyck
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From: Winnipeg, Canada
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Posts: 6,904
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Re: Starship is Go...

GW Johnson wrote:

Even once they start flying stuff to orbit,  that kind of Starship won't be the same as the kind required to go to the moon,  in turn quite different from the one required to go to Mars.  No one,  not even SpaceX,  knows what those designs will really be.

Um, could I suggest my alternative? Again? Send something a lot smaller to the Moon. A reusable lunar lander sized for 4 astronauts, parked in lunar orbit. And a Dragon capsule. It would require 2 launches of Falcon Heavy: one for the LM, one for Dragon. Rendezvous in lunar orbit. The only big catch to this is he would have to man-rate Falcon Heavy.

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#1531 2021-10-28 17:04:50

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,690
Website

Re: Starship is Go...

Robert:

I think you are quite correct. 

The vehicle you use depends upon what you really want to send.  If that is massive payload tonnage,  then the lunar Starship makes some sense.  Although it makes more sense launched from high elliptic LEO than it does from that idiotic elliptic "near halo" orbit about the moon.

If on the other hand,  it is a small crew intended to go poke around for a few days,  then a reworked LM and Dragon parked in low lunar orbit makes a whole lot more sense. 

It costs a bit more delta-vee to get into low lunar polar orbit than low lunar equatorial orbit.  But once there,  the delta vee to land and to return is only about 1.64 km/s.  From that idiotic halo orbit and the Gateway station,  it is AT LEAST 2.4 km/s one way,  just about lunar escape. 

The only reason to EVEN CONSIDER that idiotic halo orbit is that SLS block 1 / Orion can actually reach it and return!  It CANNOT reach low lunar equatorial orbit and return,  because Orion is too heavy and its service module has too little delta-vee capability.

That idiocy is EXACTLY what you get with a NASA that is micromanaged by an incompetent Congress for optimizing pork-in-district and preserving corporate welfare,  not what might actually be done. 

GW

Last edited by GW Johnson (2021-10-28 17:07:20)


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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#1532 2021-10-28 17:59:10

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 23,851

Re: Starship is Go...

We have that article on the home page and a topic of discussion on the 4 year plan that got put forward several years ago now.

http://newmars.com/2018/03/moon-direct- … our-years/

Dr. Robert Zubrin Moon Direct: How to build a moonbase in four years

All that was missing was the lunar lander

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#1533 2021-10-28 18:21:48

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 23,851

Re: Starship is Go...

The only way to get more payload to orbit after tweaking the ship is to make them expendable as you gain the mass of the return fuel not being present which is the 100mT that could be gained on top of the payload mass adjusted.

1. Mission use of the BFR/Starship is to be in the 200 million when recycled and that is not costing your payload cost and if you do not that ship cost is going to rise by another 200 million for replacement cost.

2. The cycle months of refueling losses to get it full which is 10% of the tank every month that you are not full and ready for use.

3. Then you have the difficulty of transferring that additional payload that you would want to bring to mars....

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#1534 2021-10-28 18:52:04

tahanson43206
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Registered: 2018-04-27
Posts: 8,037

Re: Starship is Go...

For SpaceNut re #1533

Re item #2 .... somewhere the idea of 10% loss of cryogenic liquid must have come up ... It keeps showing up in the forum from time to time.

There is no reason that I can see for any loss what-so-ever .... Do you have any idea where that might have come from?

It's been pointed out that a storage tank kept in the shade will chill toward's absolute Zero.

Where is the loss figure coming from?

(th)

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#1535 2021-10-28 18:55:59

tahanson43206
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Registered: 2018-04-27
Posts: 8,037

Re: Starship is Go...

For SpaceNut re #1533

Re item #3.... There is no need to transfer supplies into an aerodynamic structure once they are in orbit.

A simple truss capable of acceleration toward Mars will do fine as a payload carrier.

The payload carrier doesn't need to experience aerobraking, if it is supplied with sufficient propellant to match the velocity of Mars.

Introduction of refueling as a technique is slow to show up in planning.  That makes sense because it has not been demonstrated.

But it ** is ** a requirement for SpaceX to achieve it's objectives, so I think the chances of it coming into existence are good to excellent.

(th)

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#1536 2021-10-29 14:43:53

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,690
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Re: Starship is Go...

Large truss structures are fine for space stations with very modest propulsion requirements.  For orbit-to-orbit transfer spacecraft,  they are not so fine,  because their mass adds directly to the vehicle inert mass fraction.  Inert + payload + propellant fractions must be 1. For a given amount of propellant and a known velocity requirement,  the truss mass subtracts from payload.  There is no way around that.

What you want is to use a structure that you already must have anyway,  to serve the connection function,   or the carrying function,  of your truss.  For example,  I like to use water/wastewater tanks,  and the propellant tanks,  that I already have to have anyway,  to serve as the radiation shadow shields that my crews need. 

It's making something do double duty like that,  which is the real key to building something practical,  instead of a "Battlestar Galactica" that no one can ever afford.

I don't know what the answer is for the "payload carrier" being discussed just above,  but I'd recommend you look at what has to go,  what you have to have to move it there,  and then make "something" do double duty,  to serve also the function that a truss would have served.

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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#1537 2021-10-29 16:57:56

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 23,851

Re: Starship is Go...

Boil off occurs as you noted as a result of heat from the sun and space x has no sun shade and its not part of there design. Its not just the shade to the tank as the heat is coming from all around it. So while we may be able to reduce the boil off rate its still present and all that hand waving on repetition rate of starship fuel flights are wishful thinking at this time since we have not move any cryogenic fuels in orbit.
We also do not know the transfer rate of a starship with no pumping of those fuels to the waiting starship that's going to any destination.
This is the thruster refueling in milli-G SpaceX’s path to refueling Starships in space is clearer than it seemsStarship-propellant-transfer-Sept-2019-SpaceX-1-c-1536x796.jpg

Currently, the turnaround record (time between two flights) for Falcon boosters is two launches in less than four weeks (27 days).

Impacts boiloff

In orbit, under microgravity conditions, the propellant inside a spacecraft’s tanks is effectively detached from the structure. If a spacecraft applies thrust, that propellant will stay still until it splashes against its tank walls – the most basic Newtonian principle that objects at rest tend to stay at rest. If, say, a spacecraft thrusts in one direction and opens a hatch or valve on the tank in the opposite direction of that thrust, the propellant inside it – attempting to stay at rest – will naturally escape out of that opening. Thus, if a spacecraft in need of fuel docks with a tanker, their tanks are connected and opened, and the tanker attempts to accelerate away from the receiving ship, the propellant in the tanker’s tanks will effectively be pushed into the second ship as it tries to stay at rest.

Physics at work

The principles behind such a ‘settled propellant transfer’ are fairly simple and intuitive. The crucial question is how much acceleration the process requires and how expensive that continuous acceleration ends up being. According to Kutter et al’s 2006 paper, the answer is surprising: assuming a 100 metric ton (~220,000 lb) spacecraft pair accelerates at 0.0001G (one ten-thousandth of Earth gravity) to transfer propellant, they would need to consume just 45 kg (100 lb) of hydrogen and oxygen propellant per hour to maintain that acceleration.

100,000 kg / 45 kghr = 2,222.22 hrs / 24 hrs = 92.59 days to transfer the fuel

https://www.nasa.gov/pdf/62474main_Micr … _Guide.pdf

Nasa is working on a similar concept SpaceX begins work on Starship orbital propellant transfer test for NASAVulcan-Centuar-S2-ULA-1-1024x576.jpg

Here is the sunshade work concepts
A-Single-Launch-Dual-Fluid-Propellant-Depot-Credit-ULA-580x396.png

United Launch Alliance proposed the Advanced Common Evolved Stage, or ACES based on technology developed a few years earlier by Boeing and Lockheed Martin.

Each ACES upper stage would contain twice the propellant of a traditional Centaur upper stage booster – 41 metric tonnes of fuel. And a stretched version would have 73 tonnes on board.

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#1538 2021-10-30 09:59:52

GW Johnson
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From: McGregor, Texas USA
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Re: Starship is Go...

Shading from the sun to lower boiloff:  Don't forget the real purpose of the small "header" tanks inside the propellant tanks.  For a Starship going to Mars,  most of the propellant is burned departing from LEO.  What is needed for course correction and for landing is in the header tanks.  These are shaded by the empty main tanks,  being inside like that. Same is true for any refilled Starship returning to Earth from Mars:  most of the propellant is burned departing Mars.  Propellant for course corrections and the landing are in the header tanks. 

This is even true of Starships operating as LEO transports:  most of the propellant is burned from the staging point to orbital entry.  Propellant for orbital maneuvers,  deorbit,  and landing is in the header tanks,  shaded from the sun by their location inside the empty main tanks.  That way,  a long orbital mission is feasible without a lot of boiloff.

The unresolved problem is for the tankers that refill a Starship on-orbit before it can go to the moon or Mars or anywhere else outside LEO.  These are either another Starship flown at zero payload so as to arrive on orbit with a one to two hundred tons unused propellant,  or a dedicated tanker design carrying one to two hundred tons propellant in tanks added as the cargo section.  Those will be unshaded, and will need to be drained into the waiting vessel on a time scale of days,  not weeks or months.  (Likewise the receiving vessel needs to use its refill on a scale of days,  not weeks or months.)

There is an alternative to using attitude thrusters continuously for ullage thrust to make the transfer by microgravity.  That's going to take a lot of time and use a lot of thruster propellant. A whopping lot of boiloff will occur over a long transfer time.  There is no way to avoid that.

Settle the tanks with ullage thrust or by rifle bullet spin,  and use pumps to move the propellant quickly.  Either should work fine.  You do need the stored energy aboard to run the pumps.  But you lose a whole lot less propellant to boiloff,  by drastically shortening the time the main tanks are exposed to the sun with propellant in them.

The stored energy and/or the extra thruster propellant are just the mass penalty you must pay to do this.  But the huge boiloff loss over a long time interval is a penalty you need not pay,  if you just do the transfer quickly.  On a time scale of an hour or so. More like loading and unloading on the launch pad.

GW

Last edited by GW Johnson (2021-10-30 10:08:02)


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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#1539 2021-10-30 12:22:24

tahanson43206
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Registered: 2018-04-27
Posts: 8,037

Re: Starship is Go...

Credit surely goes to SpaceNut for repeatedly raising the boiloff concern that led to this helpful post by GW Johnson

SearchTerm:boiloff issues reviewed in post #1538 by GW Johnson - Support for shade from Sun to prevent boiloff in deep space

(th)

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#1540 2021-10-30 17:25:54

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 23,851

Re: Starship is Go...

One of the issues is customizing the launch vehicle which are all called starship at this point is one of the issues.

A lunar starship only travels from earth orbit to the moon and back as it would shed the wings and heat shield to get more mass to the moon in one vehicle that lands on the moon and required no heatshield to do so.

Lunar version

_116396334_starship_moon_astronauts.jpg

planned version with no heatshield

spacex-starship.jpg?w=594?w=650

Blue Origin recently griped that SpaceX might need with response but there is a question mark...

16 flights is extremely unlikely. Starship payload to orbit is ~150 tons , so max of 8 to fill 1200 ton tanks of lunar Starship.

Without flaps & heat shield, Starship is much lighter. Lunar landing legs don’t add much (1/6 gravity). May only need 1/2 full, ie 4 tanker flights.

Of course this is where some talk about the stripped down version being expendable for the task of refilling the on orbit ship.

Expendable Starships as Fuel Depots a NasaSpaceFlight topic

Its the ships configurations that are being mixed that will continue to be an issue...

Have been looking for the fueling timeline to get an idea of how high the flow rate is.
https://starship-spacex.fandom.com/wiki/SN15

https://nextspaceflight.com/starship/

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#1541 2021-10-30 20:33:48

Oldfart1939
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Registered: 2016-11-26
Posts: 2,250

Re: Starship is Go...

I'm guessing that there is no such thing as a "one size fits all" Starship. We are already talking about fuel tanker configurations, fuel storage depot configurations, the Lunar Lander, deep space to Mars colonization ships, freighters, etc., etc., etc.

What we are currently seeing are test vehicles--testing the propulsion systems, structural integrity, reentry and landing, and a myriad of other requirements that must be met before a human sets foot in one of them for a flight.

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#1542 2021-10-30 23:57:05

RobertDyck
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Re: Starship is Go...

I have a question. The lunar version of Starship is depicted without flaps. How does it return to Earth? It doesn't appear to have a heat shield either. How do astronauts get home?

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#1543 2021-10-31 01:30:06

kbd512
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Re: Starship is Go...

Robert,

It's an artist's depiction, but maybe they're going to do lunar orbit rendezvous?  Giant orbiting ship, plus giant lander, maybe?

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#1544 2021-10-31 08:33:36

GW Johnson
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From: McGregor, Texas USA
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Posts: 4,690
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Re: Starship is Go...

I really don't think either NASA or SpaceX have thought all the way through how the lunar variant of Starship is really going to be used.  I say that because NASA now says it will send Artemis astronauts to the south lunar pole before it finishes its Gateway halo-orbit station.  I get the distinct impression that NASA really doesn't know what it is going to do.  Meanwhile the corporate welfare programs SLS/Orion and Gateway are letting contracts and spending money. 

As I understand it,  the lunar variant of Starship has no heat shield or aerosurfaces.  It loses those in favor of tractor landing engines and regolith landing legs (which Spacex has yet to design and develop).  Supposedly,  NASA bought it to have a one-stage re-usable lander based at the Gateway station.  But I have never,  ever seen a plan for how to refill it there.  It takes a whopping lot of tanker vehicles of any kind to bring 1200 tons of limited-life cryogenic propellants at the projected mass of Gateway modules:  15 tons each.  As best I can estimate,  even a standard Starship can only bring 50-75 tons to the surface of the moon and still return to Earth. It might get nearer 100 tons to some lunar orbit,  although I have not run those numbers.

I have seen nothing credible about how to do this refill job in lunar orbit (somewhere) for a lunar Starship variant,  until the tanker/depot illustrations in the posts above,  and I don't know anything about where those came from. You can understand my skepticism. 

The only thing that makes any sense at all would be a large propellant tanker filled in LEO where Starships might bring up 100-200 tons at a time to fill it (they can ONLY bring that much to low,  eastward LEO).  The giant tanker then moves that 1200 tons of propellant as its payload (!!!) from LEO to one or the other orbit about the moon,  where it can refill the lunar Starship,  then return to LEO.  The lunar Starship never returns from the moon.

The problem with this notion is twofold:  (1) it really is a "Battlestar Galactica" (or else an entire fleet to fly in formation simultaneously) you have to build,  in order to move 1200 tons of payload from LEO to the moon,  and then also return to LEO (empty):  you are looking at 4+ km/s delta-vee one-way,  each way,  for 8+ km/s capability.  (2) the only way to reduce the size of this Battlestar Galactica is to use nuclear propulsion,  in LEO,  where "everybody" is scared of it (despite all those nuclear-powered spy satellites over the decades,  of which only one fell to Earth). 

The months of spiral-time to use electric propulsion will not be attractive at all,  because of the boiloff losses in the payload.  You just gotta fly fast.  On a regular schedule,  too.

The problem looks pretty ridiculous,  doesn't it?  Certainly does to me.  Which is another VERY GOOD reason to think neither NASA nor SpaceX have thought this thing through yet!

Just various dishes and courses for your food-for-thought "meal".

GW

Last edited by GW Johnson (2021-10-31 08:45:40)


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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#1545 2021-10-31 08:53:07

GW Johnson
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From: McGregor, Texas USA
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Re: Starship is Go...

BTW,  those landing legs on the lunar Starship variant in post 1540 above are BS.  Lunar regolith is mostly fine particulates from dust size to sand size,  with no reinforcing stony aggregate in it,  and ZERO cohesion between any of the particles of any size.  Sounds like "soft fine sand" to me.  Safe bearing load pressure for "soft fine sand" is 0.1 MPa.

Whatever lunar weight you have for your mass at landing,  you multiply that by 2 for the dynamic effects of touchdown,  and by another 2 for the effects of touching down unevenly.  Divide that factored weight by the safe bearing pressure.  THAT sizes the total area of landing pads you have to have.  And bear in mind,  numbers like that match very closely what worked quite well with the Apollo lunar module.

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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#1546 2021-10-31 18:57:17

kbd512
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Registered: 2015-01-02
Posts: 4,899

Re: Starship is Go...

GW,

What if you used electric propulsion tugs, brought tanks of CO2 and H2O to lunar orbit, and then made fuel in lunar orbit using solar power?

After you have a surface station near the ice at the south pole, then you could make propellant using the ice.

Most of Starship's methalox propellant is O2 by weight, and there's no shortage of lunar regolith to use as oxidizer.

Eventually, you'd only bring CO2 or perhaps pure Carbon from Earth.  If you find a good source of Carbon on the moon, then you don't have to bring anything except machinery to make more oxidizer and propellant.

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#1547 2021-10-31 21:12:23

Void
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Registered: 2011-12-29
Posts: 3,997

Re: Starship is Go...

I am shy to interrupt here, but I think that this may matter to your discussion.

Carbon on the Moon:
https://science.nasa.gov/science-news/s … t_lcross2/
Quote:

In addition to water, the plume contained "volatiles." These are compounds that freeze in the cold lunar craters and vaporize easily when warmed by the sun. The suite of LCROSS and LRO instruments determined as much as 20 percent of the material kicked up by the LCROSS impact was volatiles, including methane, ammonia, hydrogen gas, carbon dioxide and carbon monoxide.

I have seen articles that seem real, that indicate that there may be almost as much CO ice in the polar deposits as there is water ice.

So, some variances in the story.

However it only makes sense that if some impactors contain Carbon, and some do, that Carbon containing molecules may deposit in the ice.  After all Martian ice caps gather it at times in the North, and even more so in the South of Mars.

If this is true, it bodes well for ships with Methalox engines.

Done.

Last edited by Void (2021-10-31 21:14:09)


I like people who criticize angels dancing on a pinhead.  I also like it when angels dance on my pinhead.

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#1548 2021-10-31 21:47:49

SpaceNut
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Posts: 23,851

Re: Starship is Go...

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#1549 2021-10-31 23:27:13

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 6,904
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Re: Starship is Go...

SpaceNut: how much? Is it sufficiently concentrated to be worth mining? Enough to use as propellant?

GW: You mention boil-off. What is the boil-off for LOX & LCH4? Space Shuttle ET pressurized the LOX tank to 20 to 22 psig, and the LH2 tank to 32 to 34 psia. What is the boil-off for LOX & LCH4 when pressurized to 20 to 22 psig? Could a simple sunshade reduce heat gain sufficiently to prevent boil-off? I know it would never be enough for LH2, but what about LOX & LCH4?
Source: https://science.ksc.nasa.gov/shuttle/te … ef/et.html

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#1550 2021-10-31 23:43:31

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
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Re: Starship is Go...

You realize the arguments about mission protocol makes me want to propose my alternative again. You know: reusable LM launched into lunar orbit by Falcon Heavy. Then Dragon with crew launched by another Falcon Heavy. The trunk of Dragon would require propellant tanks and engine for TEI. Between Falcon upper stage and Dragon trunk would be a new stage, called crasher stage. That stage would have 3 jobs: Lunar Orbit Insertion (LOI), propellant transfer to LM, and deorbit LM. The crasher stage would do 90% of the work to deorbit LM and slow it's descent, then separate and crash on the surface of the Moon. The LM would have one propulsion stage only, and not detachable. That one propulsion stage would be used for both soft touch-down, and ascent. Dragon trunk, crasher stage, and LM would use LOX/LCH4. That means sufficient thermal separation between trunk and propellant tanks within so the trunk skin acts as sunshade. The LM would remain parked in Lunar orbit between missions. Subsequent missions would only require one launch of Falcon Heavy to carry Dragon with crew.

Parking the LM in Lunar polar orbit gives access to the entire surface. Each mission could land somewhere different. But once established, a Mars Direct habitat could be launched by a single Starship, cargo version with clamshell. Elon said he hopes the final version of Starship would be able to lift 150 metric tonnes to LEO. I hope that's metric. That's enough to launch Mars Direct habitat with a fully fuelled TLI stage. Launch unmanned, land on one of the poles of the Moon near an ice deposit. This would form a permanent Lunar base. The aforementioned LM could be used as a taxi to deliver crew.

Landing a Mars Direct habit on the Moon was part of the original Mars Direct proposal in 1990. Ares launch vehicle with 130 metric tonne lift to LEO was supposed to be able to inject a Mars Direct habitat into a trans-Mars or trans-Lunar trajectory in one throw. I believe that's direct launch into TMI, pausing in LEO would require more propellant. Even so, could Starship lift MD Hab to LEO with TLI stage fully fuelled, and still have enough propellant to return and land Starship?

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