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#1 2022-02-21 08:30:11

tahanson43206
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Registered: 2018-04-27
Posts: 18,142

Large Ship Chemical Propulsion

Large Ship Prime is: Large scale colonization ship by RobertDyck

This topic is offered to collect knowledge, insights and best practices for an all-chemical propulsion system for Large Ship.

"Large Ship" is (arbitrarily) defined as 5,000 metric tons, for the purposes of calculations to be posted in this topic.

It is clearly possible to deliver a 5000 ton vessel to Mars and return it safely to Earth using chemicals.

It is also (clearly) a massive undertaking. 

Fortunately, humans are good at doing large projects.

This one is on the larger size, but certainly not anywhere near the top of the chart.

This topic is intended to provide a resource for future readers/students/professionals who need to plan a flight for one of the versions of Large Ship that are in the early conceptual phases, and the customer insists upon using all-chemical propulsion.

Mission plans should include:
1) Supply of all chemicals needed (from Earth as default but other locations as they become available)
2) Launch from LEO (I'd like to see the Space Tug concept fleshed out for this) (Include "finish to Escape" by Large Ship)
3) "Docking" into orbit at Mars using chemical propulsion by the Large Ship itself
4) Launch from Mars orbit to an Earth grazing trajectory
5) Space Tug deceleration service to achieve "Docking" in LEO (no propulsion by Large Ship is needed)

A figure was provided by GW Johnson (in one of many posts) that it might take 8 tons of propellent to deliver 1 ton of Large Ship round trip.

However, that figure does NOT include the propellant needed to put the 8 tons into LEO if the source is Earth.

I'd like to see the totals for a flight of a Large Ship to and from Mars, including ** all ** fuel requirements.

Whatever that total turns out to be, atomic power can produce the fuel on Earth.

Atomic power is highly likely to find application in space because it has to much promise.

However, until then, atomic power can most certainly supply all the fuel needed for a Large Ship flight using chemicals.

I hope this topic will end up holding a treasure trove of specific knowledge needed to accomplish a round trip flight.

(th)

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#2 2022-02-21 10:28:53

SpaceNut
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Posts: 29,310

Re: Large Ship Chemical Propulsion

Space tug that uses fuel means we are expending these and dropping there incurred mass of the ship once moving of small or large starship size. The orbital insertion works the same as the in that we are firing up the engines at full power to slow the ships forward velocity but fuel volume is the limiting factor for both given how much we are trying to push or slow.

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#3 2022-02-21 10:42:50

tahanson43206
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Posts: 18,142

Re: Large Ship Chemical Propulsion

For SpaceNut re #2

Thank you for giving this new topic a running start!

For those who might not be familiar with the work of GW Johnson on Space Tugs, these are NOT expendable.

These vessels will operate in carefully designed orbits that bring them back to Earth orbit after they have released their Large Ship client. By careful design of the orbit for the Space Tug, the Large Ship will have only a trivial amount of velocity to add to achieve Escape, and thus to enter a Hohmann orbit to Mars.

It would be CORRECT to say that the chemical fuel is to be expended.

I am hoping that this new topic collects posts that prescribe accurately the amount of chemical propulsion materials needed for a single Large ship round trip from Earth to Mars, orbit at Mars, return to Earth, and orbit at Earth.

At NO time would Large Ship come anywhere NEAR an atmosphere of ** any ** celestial body.

To short cut and hopefully to eliminate concerns about energy costs to provide all the chemical propulsion material needed for a Large Ship flight, including provisioning from facilities on Earth, I propose a dedicated nuclear fission power plant.

If someone with the required knowledge/experience/skill is available in the present membership, please add a post describing the size nuclear plant required to support Large Ship missions.

This plant will need to provide all the propellant needed for launching components of Large Ship to LEO, propellant needed for delivery of supplies and equipment and the occasional on-site work person, and (of course) propellant for voyages.

An estimate of 8 tons of chemical propellant for each ton of Large Ship that makes a round trip is on the table.

This number (probably) did not include the mass of propellant needed to put the 8 tons into LEO.

I'm hoping this topic will eventually receive an authoritative post containing the exact numbers of tons of propellant needed to support the flight of a 5000 metric ton Large ship round trip.

(th)

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#4 2022-02-21 11:01:54

SpaceNut
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Posts: 29,310

Re: Large Ship Chemical Propulsion

Once fuel is expended the space tug is dead mass so it is removed from the coasting equation otherwise it slows the ship gained velocity of momentum. Plus that also reduces the energy to rotate the large ship.

Sure the space tug it will continue to coast but unless its got orbital fuel remaining its not going to make it to mars without a heat shield to slow it into mars orbit for being refueled and re-attached for reuse in mars orbit.

The large ship is entering mars orbit for disembarking as well as for reuse. It is not a cycler so its going into orbit.

Current starship is loaded with 1100 mT of fuel for escape from LEO with a starship in the order of 120 mt plus payload of 100mT with a reserve fuel of 100mT for landing on mars.

That said we know that the large ship is not landing but entering orbit.

With a starship on mars that will gain orbit to the bring those crew to mars. Sure the normal size of a starship crew is 100 but that is intended for days. So a starships taxi on mars could bring a total population of the large ship to its surface without any issues.

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#5 2022-02-21 11:10:18

tahanson43206
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Posts: 18,142

Re: Large Ship Chemical Propulsion

For SpaceNut re #4

For those who may not have had a chance to read/study the work of GW Johnson (all are available in GW Johnson Postings topic), the Space Tug is NOT a hunk of dead metal coasting in orbit.

The Space Tug is a fully awake, fully energized space vessel that is planning to slow itself to re-enter Earth orbit.

It would ** really ** help if our members (let alone readers of the forum) would take the time to study the work of GW Johnson.

That work is scheduled to be presented to the National Space Society on April 9th.

It would be helpful for NewMars members to study the work and point out any errors there might be.

I'm not expecting there will be many errors, but NewMars members should definitely try to find them.

***
To clarify a point ... the flight plan proposed by GW Johnson includes a small period of propulsion by Large ship after release from the Space Tug, to give itself Escape velocity and a Hohmann transfer orbit.

I have (by now) forgotten Dr. Johnson's recommendation for "docking" into Mars orbit. 

Hopefully this topic will attract authoritative posts giving details, but everything is available ** right now ** for anyone to study, by visiting the posts in the GW Johnson postings topic.

(th)

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#6 2022-02-21 11:26:51

SpaceNut
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Posts: 29,310

Re: Large Ship Chemical Propulsion

Space tug coasting was to mars orbit but a return to earth is also a coast once main fuel is used to give the large ship a push towards mars.

The Hohman orbit transfer is the large ship and not the tug since its long returned to earth for reuse.

That means we are using an on orbit fuel depot with this tug for the purpose of refueling on which the link for GW is
https://exrocketman.blogspot.com/2022/0 … depot.html

Is there a link on GW's site for the space tug?

A starship space tug is still very large for this push for mars escape sure its mass can be predicted for use with that depot for refueling.

Cadence_rocket-equation-earth-orbit-fig2.jpg?resize=300%2C67&ssl=1

https://www.marssociety.ca/2021/01/22/r … o-to-mars/

https://www.nasa.gov/mission_pages/stat … yanny.html

energy to get to anywhere

Cadence_rocket-equation-earth-orbit-fig4-scaled.png?ssl=1

So far all we are doing is changing where the fuel gets used.

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#7 2022-02-21 11:44:29

SpaceNut
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Posts: 29,310

Re: Large Ship Chemical Propulsion

Here is the space tug post
http://newmars.com/forums/viewtopic.php … 94#p190094

GW Johnson wrote:

I have added a worksheet to the "big ship stuff" spreadsheet that takes on tug-assisted departures and arrivals at Earth and Mars.  I used an elongated ellipse orbit for the tug with a periapsis speed just under escape.  That makes recovery and reuse far easier and more timely.  It still lets the tug shoulder the majority of the delta-vee requirements to get the ship onto the interplanetary trajectory.  What I found indicates the total propellant required of the ship plus the tugs is less than the total propellant required if the ship does all the delta-vee itself.

But,  it is not enough to make a two-way journey practical with chemical propulsion.  It still falls in the 3-4 tons propellant per ton of dead-head payload range,  for a one-way transit.  So for 5000 tons of dead head payload,  we're still talking 15,000-20,000 tons of propellant to ship up to load the ship and the tugs (if any).  At each end of the journey.  The solution is definitely high-performing nuclear and/or electric,  unless of course you opt for explosion propulsion,  which offers the most promise of all the types so far.

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#8 2022-02-21 12:18:22

tahanson43206
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Re: Large Ship Chemical Propulsion

For SpaceNut re #7 ... thanks for another helpful post in this topic!

I asked Google for help (or it might have been Yahoo) and got this link:
https://www.nasa.gov/mission_pages/stat … yanny.html

This is a NASA publication with lots of estimates of performance.

I'm going with the most optimistic, which was 85% of rocket mass is consumed to reach LEO if propellant is H2/LOX.

All the other fuel combinations were less productive (of course)

But going with the 85% figure for a moment, if 20,000 tons is needed for a Large Ship flight using chemical propellants, then 85% of X is 20,000 delivered to LEO (including the mass of the tanker).

X would be 22586 tons in this case.  i'm confident that figure is low.

The correct total should be forthcoming, when forum members have time to compute the figure.

For now, let's round up and give the total mass of propellant for a Large Ship flight round trip Mars.

20,000 (per estimate of GW Johnson) for the flight, and 30,000 (per estimate here) for lifting propellant.

50,000 tons of propellant is the grand total.  It might be less. 

Regardless, we ** should ** be able to use that figure to estimate the size of a nuclear fission reactor needed to produce that quantity of propellant in a year and a half or so.

Once in place, the entire configuration of equipment should be able to send one Large Ship to Mars every launch window.

(th)

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#9 2022-02-21 13:16:14

tahanson43206
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Posts: 18,142

Re: Large Ship Chemical Propulsion

For SpaceNut re chemical propulsion ....

The figure of 50,000 tons of propellant to make a Large Ship may be high, but it need not be though of as some kind of show stopper.

It should be possible to start accumulating some comparable figures from existing human activity....

I'm starting this follow up with a quote from Google ... I was curious to know how many tons of coal are consumed by a power plant in a year.

Whatever that figure is, it does not include the Oxygen consumed from the atmosphere, which is provided "for free" by Ma Nature.

I ** think ** the figures are for the US ... they would (most likely) show increases in India and China.

In the past decade, there has been a marked decline in the use of coal for electricity generation. Coal consumption peaked between 2005 and 2008, when over one billion short tons were used every year. ...
Characteristic
Consumption in million short tons
2019 538.61
2018 637.22
2017 664.99
2016 678.55

Can someone (would someone) add figures for individual power plants.  I'm looking for activities that consume 50,000 tons of fuel in a year.  For the purposes of this exercise, Oxygen doesn't count.

(th)

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#10 2022-02-21 13:30:21

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,615
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Re: Large Ship Chemical Propulsion

I had chemical propulsion figured for the 5000 ton "dead-head" mass using LOX-LCH4.  If the ship were assisted by tugs at each end of the journey,  it took a total of only 28,000 tons of propellant to make the round trip,  not the whole 40,000 tons.  Some (a bit over half) had to be sent up at Earth,  the rest had to be manufactured (quickly!!!) and sent up at Mars.  Call it 15,000 tons delivered to LEO,  and 13,000 tons to LMO. 

Assume for the sake of argument that a Starship/Superheavy can deliver 200 tons of propellant to LEO,  and that a Starship can deliver 200 tons to LMO.  I think the payload delivery is actually closer to 150 tons,  but let's use 200 as a nice round figure.  Delivering 15,000 tons to LEO takes something like 75 tanker flights.  Starship/Superheavy uses 4600 tons of propellant to fly the LEO mission and deliver that 200 tons per vehicle.  75 flights delivers 15,000 tons to LEO,  but uses 345,000 tons of propellant to do it.  The delivery + use total is 360,000 tons of propellant,  per big ship trip. 

At Mars,  let us again assume a Starship flight can deliver 200 tons to LMO.  To deliver 13,000 tons takes 65 flights.  Starship holds 1200 tons with which to make its flight.  That's 13,000 tons delivered by 65 flights using some 78,000 tons to do it.  The total of delivery + use is 91,000 tons of propellant per big ship trip. 

The numbers could be worse,  payload deliveries may be closer to 150 tons than 200 tons.  Double everything if it's only 100 tons.  150 tons lies in between those extremes.

We have the infrastructure to make half a million tons of propellant every year or so here on Earth.  But,  what about Mars?  You are talking 100,000 ton quantities every year or so!  Not the 1200 tons to refill a Starship,  but 1400 tons per tanker flight for 65 tanker flights,  every year or so! 

That's quite a lot of propellant to be made very quickly on Mars!  You are talking about some very major manufacturing installations to be built!

GW

Last edited by GW Johnson (2022-02-21 13:31:10)


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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#11 2022-02-21 14:31:08

tahanson43206
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Posts: 18,142

Re: Large Ship Chemical Propulsion

For Gw Johnson re #10

Thank you for taking up this opportunity!

I hope you are willing to edit your posts, such as #9, to add detail.

The NewMars database of posts is notoriously poor at saving data so it can be found easily.

I'll try to help by setting up tags:

SearchTerm:Round trip to Mars Large Ship Chemical propulsion
SearchTerm:Chemical propulsion for Large Ship round trip to Mars
SearchTerm:Propulsion Chemical Large Ship round trip to Mars

The details that I am looking for may be present, but in my first reading I missed them.

Please use the pessimistic estimates of Starship performance so we can have a better handle on actual requirements.

The result might look something like this:

1) Propellant load in Large Ship to:
    Reach Escape from Space Tug departure
    Dock at Mars
    Leave Mars without any propellant added at Mars
2) Tug propellant load to push Large Ship to just under Escape
3) Tug propellant load to catch Large Ship on return and ease it into LEO

I think I've listed everything needed at the top tier.

Below the top tier you've already provided a guide to what to expect:

1) Propellant needed to lift a given payload to LEO
2) Whatever I've missed

The grand total for chemical propulsion of Large Ship for one round trip to Mars would then sum to:

1) Load Large Ship in LEO
2) Load Space Tug in LEO (for departure)
3) Load Space Tug in LEO (for return capture)

I am making an assumption in this request, that Large Ship can carry all the propellant it needs to:
1) Reach Escape from Tug departure
2) "Dock" in LMO at Mars
3) Depart LMO for return to Earth

Your post seems to imply you are expecting to resupply Large Ship at Mars.

I would like to know if a flight without that added burden is possible.

(th)

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#12 2022-02-21 15:43:56

SpaceNut
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Posts: 29,310

Re: Large Ship Chemical Propulsion

The use of starship is a set of limits at best for fuel use and payload loading at best for any given level of payload as that is being held close to the vest by musk but they can be roughed out based on the geometric dimensions of the physical size as it currently is.

Since we can solve for the cylinder shape that can be fuel tanks and we know the ratio of the fuels used we can get close to the numbers for what is being used. Currently that stands at that 1100 mT with the 100 mT to land on mars with for the total full load of 1200 mT.

That difference in payload has to do with people versus cargo as we do not need life support and other items for cargo which gives the trade off of payload mass limits. The starship dry mass is at best 100 mT with in at its upper end 120 mT and at its lower possibly 85 mT and its that comparison (roughly 40 times bigger) that is account for the same fuels and engines that the tug requires which gives us all of the problems.

The large ship will still need course correction propellant loaded into it since the tugs are long gone for that purpose You are also hoping since these are reused that the one for earth needs to come out to meet it on the inbound course to attach to a rotating ship which now becomes problematic.

Remember that to escape earths orbit requires just about the same mount for fuel loading in the space tug to be use and then some since you are flying out from earth to catch it for the return trip. A space tug is an unmanned item and can hold more fuel as a result. So as I was saying, about them it takes away from the large ships mass to haul it to mars unless we account for it in both directions.

While mars will need less fuel to leave mars its going to need more for the breaking period for earth orbit. Then the next issue is how many trips from mars surface with a full cargo of fuel will it take to fill up those space tugs to be able to leave mars? We already have a problem for just filling up a starship and this large ship is so many times larger. Its that size of the fuel required that puts it over the edge at this point.

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#13 2022-02-21 16:12:08

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,615
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Re: Large Ship Chemical Propulsion

That nominal 28,000 tons of propellant for the tug-assisted scenario is the sum of what the big ship propulsion stage and the tug needs,  at each end of the trip.  Without the tug,  it was 40,000 tons,  20,000 sent up at Earth,  and the other 20,000 sent up at Mars. 

The numbers I was using for the Starship and Superheavy came right off Spacex's website a few months back,  when I ran the 2021 estimates.  Depending upon the details of how things got figured,  I had payload to LEO somewhere between 149 and 171 tons.  For Starship single stage to LMO and back,  payload was nearer 200 tons,  if memory serves. 

At that time,  the Starship propellant tanks were said to hold 1200 tons.  At that same time,  Superheavy's tanks were said to hold 3400 tons.  In the interval since,  I have heard noises like they were going to increase the propellant capacity of Starship a bit.  Nobody yet knows how much.  But that's where my numbers came from. 

The point off all this is not an exact estimate,  anyway.  It is to find out what ballpark you are playing in.  And I doubt anyone likes the answer.  Having to loft 28,000+ tons of propellant to orbit for each and every trip a 5000 ton dead-head payload makes,  that is not a game anyone in their right mind is going to want to play. 

If instead you try to do this with NERVA,  the no-tug version was 20,000 tons of LH2 sent to LEO for each round trip of the 5000 ton dead-head item,  none needed at Mars.  That's 4 tons per ton of dead-head.  Doubling the Isp made round trips possible single stage.  Doing tug assist might reduce that further.  I have never run the numbers.  But unless the tugs are also nuclear NERVA,  it won't buy you that much beneficial effect.  20,000 tons sent to LEO in 100-ton lots (the volume is not there to ship 200 tons of LH2 per tanker flight) is 200 tanker flights,  at nearly 5000 tons of propellant each. 

Electric was good enough to get the round trip propellant need down to under 2000 tons per round trip,  but it adds time to the voyage.  You will spend about 3 months spiraling out to escape Earth,  and 2 of those are in the Van Allen radiation belts.  You will spend about a month spiraling into orbit about Mars.  8 months Hohmann plus 4 months of spiraling is roughly a year to make the one way trip,  crudely speaking.  2000 tons of propellant in 200 ton lots is 10 tanker/cargo flights.  You'll need about 50,000 tons of propellant to send those tanker/cargo ships to LEO. 

I have no modernized estimates for the nuclear explosion drive.  Using 1957 fission technology (which does include the necessary shaped charge and reaction mass technologies),  the Hohmann round trip required something like 650 tons of nuclear devices.  At 200 tons per ship to LEO,  that's 3 or 4 cargo flights,  at almost 5000 tons of propellant each.  15-20,000 tons of propellant for those cargo flights. 

And we have yet to even discuss how to get people from LMO down to Mars.  Or up from Earth to LEO.  100 or 200 at a time in a crewed Starship?  For 1000 folks,  that's between 5 and 10 Starship flights at each end of the voyage,  just to move the people.  You also have lots of cargo to move.

We're playing in some awfully big,  expensive ballparks here.  But you can see by the trends why I recommended electric,  then gas core nuclear,  and eventually explosion propulsion.

GW

Last edited by GW Johnson (2022-02-21 16:25:31)


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 2022-02-21 18:19:18

SpaceNut
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Posts: 29,310

Re: Large Ship Chemical Propulsion

Next up is the engine count to give that much of a shove as the starship is slated currently for the 3 vacuum and 6 sea level which to burn that much fuel means we are going to need lots more of them or did I get them transposed.

So the issue is making the engine section of the large ship possible means we are building most likely with all vacuum engines some where near 60 of them and that is a large grouping for sure.

since the cluster for the first stage is only half of that to get the starship off the ground and these are all sea level units.

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#15 2022-02-21 18:47:25

tahanson43206
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Posts: 18,142

Re: Large Ship Chemical Propulsion

For SpaceNut re #14

Just a quick note of support for your proposal to install vacuum engines on Large Ship.  There would be no need for anything less.

For GW Johnson re #13 and previous posts ....

This topic is set up to wring out the all-chemical scenario.

That said, the nuclear topic might include a hybrid of chemical boost out of LEO using the Tug, followed by a nuclear propulsion system for the Escape velocity burn and any course adjustments that might be needed. Potentially, that engine system might even be able to "dock" in LMO.

The propulsion system designers have a lot of options. 

I'm (trying anyway) to guide the concentration on chemical only propulsion in this topic so we have a clean sequence for a future reader to study.

***
I'd like to see a spreadsheet or perhaps a simple text table showing an all-chemical solution with these features:

1) Lift propellants to LEO
2) Load Tug to push Large Ship
3) Load Large Ship to the gills for (a) Escape burn (b) course correction (c) "dock" at Mars in LMO (d) burn to return to Earth
4) Load Tug to catch Large Ship and ease it into LEO

That's a complete sequence without needing anything at Mars.

Can we do that?

I'm assuming the 5000 tons includes all the propellant for the orbital maneuvers other than Tug assistance.

I think it is premature to worry about supply issues until we know what is actually required.

Once we know how much propellant is needed for the entire round trip, we can attempt to assess supply procedures.

I have already tossed out the suggestion of a dedicated nuclear fission plant to make all the propellant.

Once that system is in place, it can support regular flights.

We need to know the flight requirements in order to size the plant.

***
In the 1903 time period, the idea of loading tons of aviation fuel into a 747 would have seemed like madness.  That was only 100+ years ago.

By now, we (humans) should have become used to operating vehicles that consume thousands of tons of fuel.

Per Google:

How many gallons of fuel does a container ship carry? - FreightWaves
www.freightwaves.com › News › Insights › AskWaves
Jan 15, 2020 · One of the largest container ships to call on the U.S., the CMA CGM Benjamin Franklin, carries approximately 4.5 million gallons of fuel oil.

Also per Google, 1 liter of fuel oil weights .89 Kg.
The conversion factor: gallons to liters appears to be 3.78541
4500000 * 3.78541 >> 17034345 liters so 17034345 * .89 >> 15160 tons

How about that !!! A single ocean going vessel loads up with 15160 tons of fuel oil (if I've read Google correctly)

The Large Ship is not too far beyond that now routine fuel load.

With your continued patience, we (forum readers) should soon have a (relatively) rock solid sequence to study for the chemical only option.

(th)

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#16 2022-02-21 19:03:20

SpaceNut
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Posts: 29,310

Re: Large Ship Chemical Propulsion

The central hub of the big ship would need to be built in space rather than sent up as a custom payload less fuel of course.

That would also make sending up tanks separately as well problematic since these are very large.

Maybe that hub can be split into manageable sections that could be lifted into space by a modified starship launcher.

Of course to do that needs the sea level engines as part of that trip is in the atmosphere of earth.

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#17 2022-02-21 19:08:17

tahanson43206
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Posts: 18,142

Re: Large Ship Chemical Propulsion

For SpaceNut .... do we have firm figures on the size of various components?

I'm under the impression RobertDyck is still far from ready to offer any firm numbers.

9 meters diameter (Starship hull) is quite large (by my scale anyway).

Why not simply make the vessel out of the Starships that carry building material to the assembly site?

Those stainless steel cylinders have been welded to perfection.  Why not just use them?

(th)

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#18 2022-02-21 19:40:38

SpaceNut
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Posts: 29,310

Re: Large Ship Chemical Propulsion

First removing engines during a space walk may not be possible since these would be welded in place or requiring special tools to undo the connection and or the possibility on one might cause a space suit to be torn is not so good either.

Then we do not need the passenger / cargo area of them so how would we rip that section off from the remaining let alone rewire them for use?

So how do we enclose it for shirt sleeve work would be what is needed?

Total number of remaining sections would be 28,000 / 1,200 for the number 23 plus starships needed for the tug section of the hub and you still need all of the engines and connect all of the tanks to all them so that all can fire.

The 5,000 large ring ship contained no fuel under GW's figures or minimal thruster on the ring and hub tug section mostly for rotation control.

Will all of this sending up the engines, tanks, connections and once a mounting tube for the hub is sent up for construction of the hub seems to be a better method of reduced risk.

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#19 2022-02-21 19:57:33

tahanson43206
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Posts: 18,142

Re: Large Ship Chemical Propulsion

For SpaceNut re #18

Your post covers a lot so I'll just focus on one item ... it seems (to me at least) unnecessary to have humans on site for on-orbit assembly.

Out of curiosity, why are you including them in your planning.  All assembly can be carried out by teleoperation, with operators safely on Earth.

(th)

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#20 2022-02-21 21:54:23

SpaceNut
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Posts: 29,310

Re: Large Ship Chemical Propulsion

I am not counting on robotics or any version of it as we are not developing any of it for off world use currently.
Even the man power that is used to make a starship does not currently as well and would not expect it to change anytime soon.

I need to see what a tank would mass and all other transported parts to build the space tug booster that currently is part of the main Hub for the large ship.

If I used the lower 85 mT and multiply that by 20 we are most likely close for that central Hub mass of 1700 mT. That leaves for the tunnels, ring and all of the furnishings to come under the remaining 5000 - 1700 = 3300 mT the balance.

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#21 2022-02-22 01:45:18

kbd512
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Re: Large Ship Chemical Propulsion

28,000t represents the full load displacement of America's largest amphibious warships.  This is why I discounted the use of both chemical and solid core nuclear thermal propulsion.  One-way propellant tonnages ranging from guided missile frigate to large deck amphibious ship are unworkable.  Practical specific impulse values start around 10,000 seconds and go up from there.

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#22 2022-02-22 07:41:13

tahanson43206
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Registered: 2018-04-27
Posts: 18,142

Re: Large Ship Chemical Propulsion

For all who have contributed to this topic to date .... Thank you for adding both content and perspective for our future readers!

This topic is intended to provide a solid reference for future readers who may wish to evaluate the all-chemical propulsion option for Large Ship (defined for the purposes of topic development as a vessel of 5000 tons dead mass, able to "live" in deep space for months at a time.)

While the ship (of this topic) does have propulsion capability, it is (again, for THIS topic) boosted by a Space Tug (see GW Johnson et al) for launch from LEO, and it is captured for safe return to LEO by another Space Tug. 

Thus (for the purposes of ** this ** topic) the Large Ship must provide for acceleration in five specific cases:

1) Accelerate to Escape after release by Space Tug
2) Course corrections on the way to Mars
3) Acceleration at Mars to enter LMO
4) Acceleration from Mars to return to Earth
5) Course corrections on the way to Earth

What I am hoping we will be able to provide to future readers is a table that looks like this:

Event    Mass of Large Ship   Mass of Propellant

Depart Mars   5000 tons    X1 tons (X1 includes any mass needed for course corrections)
Y1: propellant consumed by Large Ship to depart LMO for LEO plus course corrections

Arrive at Mars 5000 tons X2 tons (X2 includes mass to accelerate to enter LMO)
Y2: propellant consumed by Large Ship to enter LMO

Reach Escape Velocity 5000 tons X3 (X3 includes mass needed for any course corrections)
Y3: propellant consumed by Large Ship after release by Departure Tug

Full tanks: X4  This is the sum that includes all expenditures after Tug release
Y4: By definition, equal to X4

Space Tug Departure propellant X5 - Delivers Large Ship full of propellant to near Escape. Includes propellant to return to "home" in LEO
Y5: propellant consumed by Space Departure Tug

Space Tug Arrival propellant X6 - includes propellant needed to arrive at lock-on point, propellant to deliver both to LEO, and propellant to return to "home"
Y6: propellent consumed by Space Arrival Tug

Lift propellant X7: This is all the propellant needed to fill the tanks of Large Ship, Departure Tug and Arrival Tug

Grand total: All propellant needed for a round trip of Large Ship to and from Mars with a dead mass of 5000 tons.

It is this total that must be provided by a fission reactor designed for the purpose.

The entire business operation (not including manufacture/assembly) consists of:

1) Management structure
2) Operations staff
3) Operations activities
4) Power supply (primarily for manufacture of propellant)
5) Large Ship itself
6) Departure Tug
7) Arrival Tug

I'm assuming launch services will be provided by a third party.

(th)

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#23 2022-02-22 15:53:49

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,615
Website

Re: Large Ship Chemical Propulsion

The numbers I ran for the "big ship" propulsion study are in the word document,  the spreadsheet,  and the powerpoint slideset that I already forwarded to Tom,  and those are in the drop box,  I think. 

Those numbers define the propellant requirements for a 5000 ton "big ship" as the dead-head payload for a propulsion stage,  and as an update after the initial study,  for a "big ship" with a smaller propulsion stage assisted by tugs at each end of the trip.  The scope of that initial study was chemical (LOX-LCH4),  solid core nuclear thermal (NERVA),  generic electric,  3 different forms of gas core nuclear thermal,  and fission explosion propulsion.  The tug study was chemical only.

What I found I have already posted about,  and is well-documented in the cited documents and files.  Chemical is incapable of the two-way trip to Mars and back,  with a single propulsion stage. Period,  end of issue.  Having tug assist reduces the propellant requirements by around 35%.  NERVA is capable of the two-way trip single-stage,  but the propellant quantities are still very large.  Electric and the gas core schemes are 2-way capable,  at substantially less propellant,  albeit still large.  The only one with a "small" "propellant" requirement was explosion propulsion.  These results reflect specific impulse more than anything else.

The focus in this thread is chemical propulsion,  specifically with tug assist.  What I found with no tugs was a bit over 40,000 tons of propellants were required for the round trip:  about half sent to LEO,  the other half to LMO.  That is propellant delivered to orbit,  which is dwarfed by the propellant consumed sending it there.

What I found with tugs was a bit over 28,000 tons of propellant needed for the big ship and the tugs.  That was a bit over 15,000 tons sent to LEO,  and a bit over 13,000 tons sent to LMO.  Those figures DO NOT INCLUDE what is needed to load/unload people and cargo,  only to fuel the ship for the trip.

I have seen hints that the design of the Starship and Superheavy are evolving away from the numbers I used reverse-engineering their performances during 2020 and 2021.  Certainly there is a new version of the Raptor engine which is different from what I reverse-engineered so closely back in 2019.  Be that as it may,  the older characteristics are still "in the ballpark" for discussion purposes.  They are all that I have,  so I will use them.

Earth has a larger gravity well.  Starship can only reach LEO if launched atop a Superheavy.  The numbers I had (and worked out) say that 150-ish tons of payload can reach LEO in a Starship,  with both it and Superheavy flown reusably.  To reach LEO with full payload requires a full propellant load,  which was 1200 metric tons for Starship and 3400 metric tons for Superheavy.  That's 4600 tons of propellant consumed to deliver 150 tons of payload to LEO,  or 30.67 tons of propellant per delivered ton of payload.

Mars has the weaker gravity well.  Starship can be flown reusably single stage to LMO and back.  If memory serves,  the payload is comparable,  so call it 150 tons.  Starship holds 1200 tons,  so call it 1200 tons consumed to deliver 150 tons,  or 8 tons propellant per delivered ton of payload to LMO.

So,  consider only the refueling of the big ship in LEO and LMO,  and refueling the tugs that are in LEO and LMO.  Call it 15,000 tons of propellant sent to LEO as payload,  at 150 tons per flight.  That's 100 tanker flights,  consuming some 4600 tons per flight.  We are talking about consuming 460,000 tons of propellant to send some 15,000 tons of propellant to LEO as payload.  The total propellant requiring manufacture "quickly" is 460,000 + 15,000 = 475,000 metric tons.  And we have not yet begun to consider what it takes to send people and cargo up to the big ship.

At Mars,  we need to send about 13,000 tons of propellant to orbit.  At 150 tons per flight,  that is 86.67 (call it 87) flights.  Each flight consumes 1200 tons of propellant,  so 87 flights consumes 104,400 tons to deliver 13,000 tons as payload to LMO.  The total propellant requirement to be manufactured "quickly" is then 104,400 + 13,000 = 117,400 tons.  Exclusive of flights to load/unload people and cargo. 

My analyses are based on Hohmann min energy transfer at average planetary distances from the sun.  That's an 8.6 month one-way voyage.  I had it figured for about 13 months at Mars before embarking on the voyage home to Earth. The total round trip is about 30 months,  so you have about 22 months waiting in LEO before the planets line up again.

At Earth,  you have 52 months to make 475,000 tons of propellant for a trip like this every other time the planets line up.  That's 9135 tons per month steady manufacturing rate.  With the infrastructure we already have on Earth,  that's doable,  just expensive.

You have the same 52 months on Mars to make 117,400 tons of propellant.  That's 2258 tons per month steady production rate.  We're currently worried about making 1200 tons in a year,  so this kind of production,  and the infrastructure that supports it,  are many years (more likely decades) away.

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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#24 2022-02-22 18:31:52

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 29,310

Re: Large Ship Chemical Propulsion

GW, Is it possible to use the engines in a more powerful ion like mode where we are looping outward and making use of gravity assists with a throttled back fuel use.

Since the ship has the protection passing through the belt should not be an issue rather than a bruit force escape firing. Sure its going to be a longer trip time but it seems possible.

trajectory-design1.jpg

The current course correction are done with thrusters that are way smaller than those that we need for the tonnage that we are expecting to move.
here is the details for the trajectory correction maneuver (or TCM) to fine-tune its landing point for marsoq5xmHanUC9qRvqnqlPOLvKsur_IpRCeKQvgF6omXinKcC-o-lpTRjDGXqe_fYKh3xGQghiAsNuhIqcBTF9o6FcsLpKAx6ulgzUjts4xDYbAL6GzhviwLJ6qCh4gkTEfJL0-I6bh

I am not sure if there is more or less for our trajectory to mars.

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#25 2022-02-22 18:59:00

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,142

Re: Large Ship Chemical Propulsion

For GW Johnson re Post #23

It appears we have no one in the forum (other than me) who wants to learn how to compute space flight propellant requirements using your tools.

You have been offering those tools for several years, and I am the ** only ** member who has shown any interest.

You ** could ** teach 1, 10, 100 or thousands of people a fraction of what you know, but at the moment, we are batting zero in trying to find students.

Your presentation at Houston is an opportunity to break through. 

In the mean time, I appear to be all you've got to work with.

I'm going to quote a line from your post ... let's concentrate on that line:

At Mars,  we need to send about 13,000 tons of propellant to orbit.

I assume ??? that this 13,000 tons is for Large Ship to burn to leave LMO and decelerate in order to fall back to Earth.

Or is that 13,000 tons for a Tug at Mars?

In your reply, please refer to the post: #25

(th)

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