Musk Mars Society interview

louis · 2020-10-17 19:18:06

Surprised I can't see any thread on this topic. SpaceXcentric has a vid on the interview - looks like Zubrin might have been asking the questions.

Most interesting part: Musk says non human cargo flight to Mars could take place in 2024. So think that's the first time he's announced a two year slippage on the original timescale. Means earliest for humans on Mars is probably 2026 or 2027.

Last edited by louis (2020-10-17 19:18:53)

kbd512 · 2020-10-17 20:58:33

Louis,

I still think early 2030s is the most realistic first crewed flight to Mars. SpaceX is going to encounter design challenges along the way that push that first flight a little further into the future. I believe they will still get there, just not as soon as everyone had hoped.

SpaceNut · 2020-10-18 08:25:56

Sure we can deliver cargo to mars for any selected site but the limits of that cargo and amount of drift is dependent on the landing format of parachutes, heatshield, propulsive landing rockets, pressurized as well as unpressurized cargo shell features.

Going with what we have now is a 1-2 tons to something less than 10 tons at best once we strip out any of the current delivery systems.

what we deliver must be self contained to extend the life cycle of the goods that we deliver to the Mars surface. That one feature can eat into the deliverables possible payload mass.

Void · 2020-10-18 08:27:47

Maybe something like this?

https://www.msn.com/th-th/video/other/w … i-BB1a7HwV

SpaceNut · 2020-10-18 13:38:06

I hope others saw that the zoom interface was on pages full of Arabic...
Need to find another more protected video source to actually watch....

louis · 2020-10-18 17:54:20

Given their Apollo rate of progress I think 2026/7 is doable.

kbd512 wrote:

Louis,
I still think early 2030s is the most realistic first crewed flight to Mars. SpaceX is going to encounter design challenges along the way that push that first flight a little further into the future. I believe they will still get there, just not as soon as everyone had hoped.

louis · 2020-10-18 17:57:09

SpaceNut wrote:

Sure we can deliver cargo to mars for any selected site but the limits of that cargo and amount of drift is dependent on the landing format of parachutes, heatshield, propulsive landing rockets, pressurized as well as unpressurized cargo shell features.
Going with what we have now is a 1-2 tons to something less than 10 tons at best once we strip out any of the current delivery systems.
what we deliver must be self contained 5to extend the life cycle of the goods that we deliver to the Mars surface. That one feature can eat into the deliverables possible payload mass.

Er - we're talking Space X here. Forget about parachute landings - this is 100 tons to the surface of Mars.

SpaceNut · 2020-10-18 19:18:15

Believing the hype rather than the here and now... Elon Musk says SpaceX's 1st Starship trip to Mars could fly in 4 years

That window Musk referred to is a launch opportunity that arises every 26 months for mission to Mars.
The next window opens in 2022 with Musk referring to the 2024 Mars launch opportunity.
This year, SpaceX launched two test flights of Starship prototypes, called SN5 and SN6, from its Boca Chica test site in Texas. Those flights reached an altitude of 500 feet (150 meters).
SpaceX is currently preparing another Starship prototype, called SN8, for a 12-mile-high (20 kilometers) test flight in the near future.

https://www.newshables.com/2020/10/18/e … n-4-years/

https://youtu.be/y5Aw6WG4Dww

https://spaceflightnow.com/2020/09/01/e … ga-rocket/

With the nose cone added, the Starship vehicle will reach a height of around 164 feet, or 50 meters. The vehicle measures around 30 feet (9 meters) in diameter, about one-and-a-half times the diameter of a Boeing 747 jumbo jet.
For orbital missions, Starship will fly as the upper stage on top of the massive Super Heavy first stage booster. Combined with the Super Heavy first stage, the entire stack will stand around 394 feet (120 meters) tall, according to SpaceX’s website.
Both stages will come back to Earth for propulsive landings, much like the first stage on SpaceX’s partially reusable Falcon 9 rocket. That will make the Super Heavy and Starship fully reusable.
SpaceX says an operational Starship could haul more than 100 metric tons, or 220,000 pounds, of cargo to low Earth orbit, more than any rocket since NASA’s Apollo-era Saturn 5 launcher.

What is the BFR stage targeting for vales

Musk previously said the Super Heavy booster would have more than 30 methane-fueled Raptor engines, but Musk said Monday SpaceX is trying to “simplify the configuration.”
“So it might be 28 engines,” Musk said. “That’s still a lot of engines. We’ll also end up cranking up the thrust on the engines.”
An outer ring of engines on the Super Heavy booster will have fixed nozzles, while an inner group of eight Raptors will vector their thrust to steer the rocket during takeoff and landing.
Over time, the outer row of engines could each generate around 300 tons, or about 600,000 pounds, of thrust, according to Musk. The inner eight engines will each produce about 210 tons, or 420,000 pounds, of thrust. That will give the Super Heavy more than 15 million pounds of total thrust at liftoff.

what it will take to get from orbit to any place other than back down

GW Johnson · 2020-10-19 09:07:04

The 19 Oct "Daily Launch" email newsletter from AIAA had several items, related to this topic and some others. Here's a summary.

Starlink launch with Falcon-9 successful. Booster flown 6th time. Landed on drone ship. Both fairing halves also caught. Opinion: Bravo!

Launch abort Falcon-9 from 2 weeks ago with USAF GPS satellite still under study. Considered a prerequisite to resolve before next crew launch. Crew launch now set for mid-November. Opinion: keep your fingers crossed!

NASA's probe set to attempt retrieval of surface sample tomorrow from asteroid Bennu. Opinion: Keep your fingers crossed!

Musk talks about Starship/Superheavy (at Mars Society convention). Says "fighting chance" to send first uncrewed mission to Mars in the 2024 window. Says they could be attempting on-orbit refueling in 2022. A quote: However, “he conceded that his estimated dates for the rocket’s progress ‘are just guesses, obviously,’ and may change.”

My opinion: they would be lucky indeed to make those dates. There has been some improvement recently, but the observed ratio of actual time to Musk time has been at or above 2. Opinion: first uncrewed closer to 2028, first crewed in early 2030's. Still way of NASA's most optimistic projections.

GW

SpaceNut · 2020-10-19 19:32:07

When we look at the starships for performance on mars empty and needing to be refueled since it las empty after making use of the internal landing reserves off 100 ton fuel source. One must assumes since we are landing a starship from earth orbit that that is what must be held onto for the earth return once the ship makes orbit around mars.
That said what amount of fuel do we need above the known 100 ton to get a starship back to orbit from a mars surface?

GW Johnson · 2020-10-20 08:50:40

Well, I never looked at Starship to Mars orbit from Mars's surface. Can't give you a number. But I have looked at Starship to and from Mars as direct flights, multiple times. The result is very sensitive to the inert mass of Starship, which is likely closer to 120 metric tons than the old 85 ton value.

Remember, this thing is first a transport to and from Earth orbit. The tonnage of propellant required to deorbit and land is sensitive to inert mass as well as return cargo mass (which would include any crew and passengers). My numbers usually fall between about 10 to about 25 tons of propellant.

It launches atop the Superheavy, both of them full of propellant, and that's about 1200 metric tons for Starship, 3300 metric tons for Superheavy. You arrive in LEO with maybe 100 tons of cargo, and around 20-ish tons of unused propellant. If the inert mass drops by 5 tons, you can carry 5 tons more cargo. Etc.

It cannot leave LEO unless refueled there. I'm showing it must have the full load of 1200 metric tons of propellant on board to go to either the moon or Mars, with about 100 tons of cargo and that 120 tons inert mass. They keep showing 4 tanker flights in their illustrations, but I keep getting 6-9 tanker flights required with my best guesses for their unpublished tanker designs. So there's a disconnect there between what I analyze, and what they have in mind.

The moon must be flown without refueling on the moon. You have to depart at about lunar escape speed, with 10-20 tons of propellant still on board for the landing.

My analyses may be slightly conservative, because I keep throwing in course correction burn allowances. But regardless, I'm in the ballpark with them. But, I am NOT allowing for cryogenic propellant evaporation losses, and that is definitely NOT conservative! So I may really be underestimating propellant requirements (and overestimating cargo capacity) for the long flights to and from Mars.

As for returning from Mars, you have to fully refuel the Starship to its 1200 ton propellant capacity. The notions of ~50 ton return payload and 120 ton inert mass require that, whether you fly 8.5-month Hohmann return, or the slighter-higher energy 6 month return, which seems to be their preference now. You have to arrive at Earth with ~20 tons propellant to make the landing.

It is the free return at Earth that is the most demanding in terms of heat shielding. Depending upon your trajectory, velocity at entry interface is 12-17 km/s. Earth escape is 11 km/s. Return from LEO is at 8 km/s. Mars entry, depending upon trajectory, is 7.5 to 9 km/s, with Mars escape 5 km/s. (Entry from low Mars orbit would be about 3.7 km/s.)

Any two-way trip to Mars and back will have to endure a 7.5-9 km/s entry at Mars, followed by a 12-17 km/s entry at Earth, all without refurbishment, and with 2+ years of weathering outside in the environment on Mars. Including erosion by dust storms. Just something to think about.

They have a lot of things to think about, beyond just getting Starship to reach Earth orbit in flight test without growing its inert mass past 120 tons. There's also the landing stability and soil penetration issues I have raised about the landing leg designs so far. Plus all the other stuff I just mentioned above.

It's dealing with stuff like that which is a part of the reason actual time/Musk time is still nearer 2 than 1.

GW

Last edited by GW Johnson (2020-10-20 09:04:43)

kbd512 · 2020-10-20 10:57:56

GW,

They need to think about building real interplanetary spaceships in LEO that use some form of advanced nuclear electric propulsion. The ratio of propellant burn to payload delivery is 550t of propellant for each 1t of payload delivered. That kind of burn is grossly impractical for establishing a colony with a million people. A practical solid core nuclear thermal rocket engine could cut that fuel burn in half. An even more practical nuclear electric, ion or fusion drive, would reduce that by about an order of magnitude.

1.5t wet mass, 1t dry mass
dV @ 381s = 1,515m/s (LOX/LCH4)
dV @ 450s = 1789m/s (LOX/LH2)
dV @ 900s = 3579m/s (NTR/LH2)
dV @ 5000s = 19,881m/s (Ion or Fusion Drive)

42t of propellant per ton of delivered payload seems doable, whereas 550t is probably not sustainable in the long run. If each person sent represents a 2t payload investment, that translates into 84,000t of propellant vs 1,100,000t of propellant, or around 695 million gallons of LNG. The Aluminum propellant would cost $156M at current prices, whereas 695 million gallons of LNG would cost $2B at current prices, or $156 per person vs $2,000 per person. I expect total cost would be about like purchasing a business class airline ticket to an intercontinental destination. Now presume that a more realistic mass allocation per passenger is more like 10t, not including the mass of the interplanetary spaceships that have to be built. That's why we need better propulsion. The required mass allocation is likely to be far greater than anticipated.

Elon Musk said we need an exponential rate of innovation, but what he actually needs is an exponential propellant mass reduction so that tickets cost about as much as a business class airline ticket. That way, there's money left for all the hardware required to keep people alive on another planet. We're going to construct and deliver a lot of steel cans for people to live in, similar to those bunker homes that preppers bury underground. As soon as we can construct those on Mars to reduce the required reentry mass, we won't spend money on that, either.

SpaceNut · 2020-10-20 17:42:35

Earth entry
Starship-reentry-Earth-SpaceX-1-crop-5-edit-1-1024x549.jpg

Low Earth Orbit (LEO), Starship will be traveling no less than 7.8 km/s (Mach 23, 17,500 mph) at the start of atmospheric reentry.

Earth landing

https://www.spacex.com/vehicles/starship/index.html

https://www.spacex.com/media/WebsiteSta … sktop.webm

Starship will enter Mars’ atmosphere at 7.5 kilometers per second and decelerate aerodynamically. The vehicle’s heat shield is designed to withstand multiple entries, but given that the vehicle is coming into Mars' atmosphere so hot, we still expect to see some ablation of the heat shield (similar to wear and tear on a brake pad). The engineering video below simulates the physics of Mars entry for Starship.

1

Earth entry slow down is about 15 minutes followed by the landing cycle of about 10 minutes for a verticle landing.

Mars slow down needs multiple entries to air drag to burn off that speed with the heat shield of which we will get less time for the landing to take place in duration.

https://medium.com/spaceinmylifetime/ho … 38bcc2aefe

Refueling is a big one. The mission profile for a Starship traveling to Mars consists of the following phases:
1.Launch from Earth with Mars-bound payload, arriving in orbit with dry tanks
2.Refuel in orbit with multiple Starship tanker launches and rendezvous, topping off the tanks
3.Transfer orbit to Mars and land on Mars without orbital insertion.
4.MISSION
5.Refuel on the surface of Mars.
6.Launch from Mars and transfer orbit to Earth.
7.Land on Earth without orbital insertion.
Starship methane fuel mass: 240,000kg
Hydrogen portion of fuel mass: 240,000kg * .25 = 60,000kg
Starship Payload to Mars: 100,000kg
Bringing the hydrogen along would consume two-thirds of the payload capacity, but is doable.

tahanson43206 · 2020-10-20 20:26:03

For SpaceNut re #13

Just curious ... did the source you quoted include mention of oxygen?

I followed the link but it did not seem to be about the SpaceX mission plan.

I did see the quote about taking hydrogen along.

(th)

GW Johnson · 2020-10-21 14:38:38

I don't think you've got the right numbers for return propellant from Mars in post 13 above. It takes a full propellant load of (as currently thought) 1200 metric tons, which is 1,200,000 kg of propellant. About 3/4 of that is oxygen (some 900 tons = 900,000 kg), and about 1/4 of that is methane (some 300 tons = 300,000 kg). Those numbers are exact for r = 3. Theirs is closer to r = 3.5 maybe 3.7, I think. But the numbers are that ballpark. And nothing about those numbers is anywhere close to 240,000 kg = 240 metric tons of anything.

And as Tahanson 43206 noted, there is nothing about the oxygen, which dominates by far.

GW

SpaceNut · 2020-10-21 19:11:33

The 240,000 kg is just the methane with no oxygen of which I did see the 3.8 ish number for ratio of oxygen to a methane.

Rich is typical so let it be 4 x 240,000 = 960,000 of oxygen

960,000 + 240,000 = 1,200,000 kg of which originally that number was 100,000 kg to low to land with and most likely its even more if the tanks are not keeping boiloff low enough for the duration of the trip. I would hate to not have enough landing fuel for mars once we get to orbit after slowing down for mars entry....

GW Johnson · 2020-10-22 09:08:35

As far as I can tell from Musk's presentations, the plan for Starship at Mars is direct entry from the interplanetary trajectory, not ever stopping in low Mars orbit, or any other orbit at Mars. My reverse-engineering numbers say that they cannot carry enough propellant to make an orbit-entry burn. Most of the 1200 tons of propellant is used leaving Earth orbit, a bit is lost to evaporation of cryogens along the way, there might have to be a course correction burn, and they need to save back around 20-50 tons for the landing.

Why that much for the landing? My bet is they will find they have to light earlier (to aid the pull-up maneuver) and burn more, in order to reliably land in that thin atmosphere. Their own simulations show end of hypersonics in the 5 km altitude range, just about like I thought. You are seconds from supersonic impact unless you can bend the trajectory upward. I think the air is too thin to do that with only lift forces, even on lowland plains.

Much of the oxygen has to come from electrolyzed Martian ice. There is no other practical source. The hydrogen from that goes to the Sabatier reactor to make methane, using the carbon from atmospheric CO2. Which is why they need to mine subsurface ice in massive deposits, rather than process tons of slightly-damp regolith to make ounces of water. NOT practical!

Sending hydrogen to Mars to make methane from a Sabatier reactor is what you can do unmanned. Mining ice is going to take men. PERIOD! Unfortunately, until you have men there to mine ice, your propellant production rate will be slower, and you won't ever have enough oxygen. I have seen no proposals for robot devices that would get around this problem.

It's chicken-and-egg, which is what no one, not even Musk, will face up to. You need to be able to make the return propellant robotically, before you send the men. But you have to have the men there to mine the ice, or you will never make enough return propellant.

I'd like to see them succeed, and the sooner the better. But I am skeptical of the propellant-making capabilities that are required for this transportation system not to be a one-way suicide trip.

GW

Last edited by GW Johnson (2020-10-22 09:20:32)

kbd512 · 2020-10-22 17:33:27

GW,

There's a third option. You implement some version of Lockheed-Martin's Mars Base Camp so you can remain in orbit to tele-robotically scour the surface, looking for shallow ice deposits to mine, to include a propellant tank to determine the feasibility of water extraction and transfer, a sort of mobile drill rig. Then and only then do you bother landing the propellant plant. After that you land the propellant plant on that block of ice, you begin industrial scale water extraction for transfer to the propellant plant Starship. After you have sufficient purified liquid H2O and purified liquid CO2, then you need to tele-operate the propellant plant to produce propellant in batches. Once you have sufficient propellant to transfer a load into an empty crewed Starship, then you can make the assumption that this process will continue to work successfully and land the crewed vehicle. I still think it would be best to only use Starship as a crew and cargo transfer vehicle on both ends, leaving Starships on Mars and Starships on Earth. The moon is so close that immediate return is possible, but even there if the plan is to operate a permanently occupied base, then they need to operate as transfer vehicles. We need tanker trucks to make runs between the propellant plant and a crewed Starship a few kilometers away. You don't want the base, the propellant plant, and the landing area for the crewed Starships to be co-located. You do want reliable heavy duty vehicles that can make regular milk runs between the three, carrying water, propellants, replacement parts, repair or monitoring crews, etc. The cryo-plant won't be permanently occupied, though. It'll have to be something you visit after each batch of propellant has been completed to inspect seals, pumps, etc.

GW Johnson · 2020-10-23 09:05:13

Kbd512:

Your third option makes a lot of sense. But it cannot be executed using Musk's Starship. The delta-vee capability is missing from that vehicle to stop in Mars orbit.

I looked at Starship to perform the same surface to low orbit ferry function on Mars that it plus Superheavy will do Earth. It can do that. But it cannot fly from LEO to LMO. Not even at zero cargo load.

Sorry. Your option will require a different vehicle or transportation system.

GW

tahanson43206 · 2020-10-23 09:43:07

For GW Johnson and kbd512 ...

Thank you for the discussion you are having!

Please evaluate a Fourth Option .... Refuel the Starship as now planned, but instead of using ** that ** fuel (and oxidizer) to boost to Mars, use an orbital tug to provide the Earth Departure boost. ** That ** vehicle would be comparable to the heavy booster that is going to put Starship in orbit, but ** much ** smaller. It would remain in orbit to perform this simple duty over and over.

The number of tanker loads would increase. The number of tanker loads might even double. But ** that ** expenditure is only for expendable chemicals.

The result would be a fully fueled Starship arriving at Mars with plenty of fuel for maneuvers and even for landing if that is desired.

(th)

SpaceNut · 2020-10-23 19:38:35

The issue is the payload capacity (100 mT) for fuel being the cargo is the cost of the tank to hold the fuel cuts into the amount we are delivering to a waiting starship that needs refueling.
Since the ship needs a 1,200 mT load to go to mars and it has onboard for deorbit burn and landing of 100 mT as reserve that counts against the refueling need of 1,000 mT making 11 payload cargo carrying fuel ignoring the tank mass to allow for the trip to happen with of course less for moon missions.

GW Johnson · 2020-10-24 09:51:42

I've got Starship/Superheavy pretty-well reverse engineered as of Musk's 2019 numbers, over at my "exrocketman" site. That would be the 22 October 2019 article titled "Reverse-Engineering the 2019 Version of the Spacex “Starship” / ”Super Heavy” Design". In it, I cover getting to LEO, going to Mars, and free-returning from Mars. I did look at going into LMO before landing on Mars, but you have to land or you cannot refuel. That drastically cuts deliverable payload by the very impractical factor of 4.

I also looked at using Starship as a surface to orbit-and-back ferry vehicle based (and refueled) on Mars. That's the 16 September 2019 article titled "Spacex "Starship" as a Ferry for Colonization Ships", which might be of interest to RobertDyck and Tahanson43206. Not directly for the giant colony ship they are looking at, but as the transfer vehicle from it to the surface.

For anyone wanting to know what the Raptor engines can do when operated at full design chamber pressure, I have all those ballistics worked out in the 26 September 2019 article titled "Reverse-Engineered “Raptor” Engine Performance". The scope there covers both the sea level 40:1 bell and the vacuum 200:1 bell. Both use the same powerhead. I've got plots of performance vs altitude for both versions.

GW

Last edited by GW Johnson (2020-10-24 09:53:23)

SpaceNut · 2020-10-24 11:28:16

Starting with GW's Analysis of Space Mission Sensitivity to Assumptions
using the dates in the above post by GW.

First up is boiloff lose rate of which we are capable it seems of using a cryogen cooler to achieve near zero lose rates and hoping that that is part of the Starships design....
NASA cryocooler technology developments and goals to achieve zero boil-off and to liquefy cryogenic propellants for space exploration

https://www.esa.int/Enabling_Support/Sp … onstration

Agreed that engine out needs to be considered early until we have more engine flight data or more testing to prove out the engines capability after being in orbit for so long while refueling and then drifting to mars to be used for the landing phase. Of course the first refueling and landings of the cargo ships will give a good chunk of data for the engines use for mars long before we start out.

These landings and relaunch of used ships will also give the cycle times for reuse and give a good look at the heatshields resistance to failure for mars as well.

GW Johnson · 2020-10-24 13:34:54

I got to looking, and I had updated my estimates of Starship / Superheavy again this year. These would reflect the 120 ton inert mass for Starship per Musk at Boca Chica. Performance levels are a lot lower at the higher inert weight.

The surface/LEO two stage trip, and the exploration of possible tankers, is in the 25 May 2020 article titled "2020 Reverse-Engineering Estimates for Starship/Superheavy".

The revised Mars trip estimates are in the 21 June article titled "2020 Starship/Superheavy Estimates for Mars". This included looking at stopping in low Mars orbit.

I looked at the moon mission unrefueled, with the 120 ton inerts, in the 5 July 2020 article titled "2020 Estimates for Spacex’s “Starship” to the Moon". Unlike the 2019 numbers, this didn't look feasible anymore at the higher inert.

So, I looked at launching the Starship that lands along with uncrewed tankers, doing refueling in the vicinity of the moon. That was more feasible, although the number of tankers to LEO is very large. This was the 13 July 2020 article titled "Non-Direct to the Moon with 2020 Starship".

The heavier inerts make a huge difference in the performance levels you can get out of the "Starship" and "Starship/Superheavy" configurations. There is no way around that. But if they get the inert weight down nearer Musk's goal of 100 tons, the performance lies between what I calculated in 2019, and what I calculated this year.

GW

SpaceNut · 2020-10-24 17:17:59

With a heavier starship we would need a more powerful first stage BFR to get the beast to orbit. The trouble with optimizing is the trades made for more engines require more fuel in that stage to get the performance desired from the starship payload capacity.

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Musk Mars Society interview

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