Starship is Go...

Oldfart1939 · 2020-08-25 12:18:35

With the improvement in thrust from the Raptor engine, The Isp is finally approaching that theoretical figure of 330 sec.
I'm not sure about the weight of these vehicles, but restating the third law of thermodynamics in another perverted form: things will get heavier before they get lighter. I do look forward to the 20 km test hop by SN8. It shouldn't look like a flying silo by then, since it's been stated it will have a nose cone and flight control surfaces (fins).

Last edited by Oldfart1939 (2020-08-25 12:19:50)

louis · 2020-09-04 16:43:29

So SN6 did its hop-thing! Great news!! Looks like Starship is going from strength to strength. Elon says they are starting on the build of the Superheavy in the next few days.

SpaceNut · 2020-09-13 20:55:36

Starship SN8 is to become the next prototype vehicle to undergo a test flight. CEO and Chief Designer Elon Musk confirmed a readiness schedule for the vehicle that will fly with three Raptors, a nose cone, and aero surfaces.

The update is an advance on SpaceX’s previous test schedule that was set to conduct multiple hops with SN5 and SN6. Following two successful 150 meter hops, SN8 will be launched to 60,000 feet (18.2 KM) as early as October.

GW Johnson · 2020-09-14 12:08:18

The Sea level Raptor is rated at max thrust as 2 MN, and just about 330 s Isp. It's actually slightly less than 2 MN, but let's ignore that.

3 Raptors totals 6 MN total thrust at max thrust setting. Musk said at Boca Chica that for operational Starship/Superheavy launches, they want a takeoff thrust/weight ratio of 1.5, in order to get the trajectory kinematics they want. But for a simple hop test to 60 kft, let's assume thrust/weight only 1.2 at takeoff. That's still a decent 0.2 gee vertical upward acceleration off the pad.

That means the takeoff weight is 6 MN / 1.2 = 5 MN = the Earth weight of some 509.9 metric tons. Call it 510 tons at 2 significant figures. That's the max liftoff mass those three Raptors can lift at full thrust with a (presumed) adequate thrust/weight.

Musk also said at Boca Chica that the Starship prototype designs were running 120 metric tons inert dry mass. He said the goal was 100 tons. Not having flown yet, they would still be a long way from that goal. So assume the 120 metric ton inert dry mass figure.

Now, also assume zero payload. This is an early test flight. Inert + payload + propellant = ignition mass. We have a limit on ignition mass for this test, so the propellant cannot be anywhere near a full load. The max propellant they can carry for this test is 510 tons igition - 120 tons inert - 0 tons payload = 390 tons of propellant. So the nominally-1200 ton tanks are nowhere near full.

Now, I get a flowrate of 0.6 metric tons/sec propellant flow rate through a Raptor at 2 MN full thrust (at full thrust setting and 330 s Isp). For 3 Raptors at full thrust, that is 1.8 metric tons of propellant burned per second.

If the entire test were flow at full thrust (and it will not be), the 390 tons of propellant would last for only 216 seconds. Bear in mind that both propellant flow and Isp reduce as you throttle back from full thrust. At reduced thrust through much of the trajectory (up and down!), this test might run somewhere around 300-400 seconds. That's just a guess.

Toward landing, with the tanks nearing empty at, say, 130 tons (1.3 MN weight) of vehicle, then at the same 1.2 thrust/weight margin, they only need about 1.5 MN of thrust. They could land on one engine at 75%, or all three throttled to 25%. 20% would a thrust = weight touchdown with all 3 engines running.

What I have seen published about the Raptor is that the min-throttle condition is 20%. These 20-100% limits are imposed by flame blowout inside the powerhead. They actually have reached the 100% setting in tests now.

My guess is that they will shut down 1 engine and land on two for redundancy. Those two would be operating in the 31-38% range. If one flames out, the other could throttle up to 62-76% to handle the touchdown.

Beyond that, what speeds they attempt and how they descend are unknown to me. If it were up to me, I'd go up slow (probably subsonic all the way), and just do a descending hover from there to a touchdown.

120,000 feet of path length (60,000 up, 60,000 down) at an average velocity of 500 ft/s (just under half the speed of sound), is a 240 sec flight. In a gross sense, that's just about right, if most of the flight is done at reduced thrust.

GW

Last edited by GW Johnson (2020-09-14 12:14:25)

Oldfart1939 · 2020-09-14 18:51:14

Well--in any event, this first 60k ft should be nothing less than spectacular. I don't recall if Musk stated there would be a "skydiver descent" on this first flight or not.

Oldfart1939 · 2020-09-14 18:52:19

Stay tuned tonight for the SN 7.1 pressure test; road closure is in place starting at 21:00 hrs CDT.

Oldfart1939 · 2020-09-15 20:01:57

3 Tanker Truckloads of liq N2 arrived today in Boca Chica. Something is imminent!

SpaceNut · 2020-09-16 20:03:50

No news yet

Sure looks ugly...

Oldfart1939 · 2020-09-18 11:15:51

The pressure test to burst pressure of SN 7.1 was scrubbed last night (09/17/2020). Tonight is another possibility, since the road closures are still in effect.

louis · 2020-09-18 18:17:05

Interesting video on Felix's "What About It?" You Tube channel - looks like Space X are now using their Florida site to test a 1 MW methane production facility (obviously to facilitate fuelling of a return to Earth flight for a Starship). This is marvellous affirmation of seriousness of intent. I don't think we can yet rule out a cargo flight to Mars in 2022 with human flight in 2024.

Musk is achieving Apollo style pace of development. We could see orbital Starship flight jn early 2021.

So maybe they are planning to ship a fully operational methox plant to Mars in 2022!

One thing about space - as long as you can get into orbit and fire your engines, the cosmos is pretty much your oyster. It's not like getting to Mars is really any more difficult than getting to the Moon as far as the transport system goes. As long as you have comms in place they are much of a muchness.

Oldfart1939 · 2020-09-18 19:48:35

Louis-With all the activities at Boca Chica, many of the side projects aren't even noticed by most SpaceX watchers. The facilities in Florida haven't had much scrutiny recently. It won't be many more months and the Moxie unit on the latest NASA rover will begin operation. It's like a jigsaw puzzle with widely scattered pieces.

louis · 2020-09-19 18:47:47

Yes the jigsaw puzzle is a good analogy. Space X's focus on developing a methox production facility suggests that plans for other essentials such as habs, energy production and surface transport and mining capability may also be well advanced.

Oldfart1939 wrote:

Louis-With all the activities at Boca Chica, many of the side projects aren't even noticed by most SpaceX watchers. The facilities in Florida haven't had much scrutiny recently. It won't be many more months and the Moxie unit on the latest NASA rover will begin operation. It's like a jigsaw puzzle with widely scattered pieces.

louis · 2020-09-26 07:19:27

The "What About It?" You Tube channel (presented by Felix) has a great update video. Highlights for me were a glimpse of the first section of the SuperHeavy and an interesting illustrated discussion of possible landing leg designs for the Starship.

Last edited by louis (2020-09-26 08:10:11)

louis · 2020-09-26 08:23:34

Here's the "What About It?" link...

https://www.youtube.com/watch?v=tG8KiXQahcg

louis · 2020-09-30 18:23:57

Another good vid from WAI (Felix).

https://www.youtube.com/watch?v=tG8KiXQahcg

SpaceNut · 2020-10-11 17:22:33

SN8 receiving Raptors as prelude to advanced Starship testing] and hoping for a test flight to 50,000 feet.

SN8 underwent a total of three cryo proofing tests during the week. The first was deemed acceptable per the test parameters, but a small leak “opened up near the engine mounts, possibly due to differential shrinking,” according to SpaceX Chief Designer and CEO Elon Musk.
The repair was completed in time for a second test the following night, which appeared to show SN8 fully loaded with LN2 (Liquid Nitrogen), but without any reference as to how it went from Elon. Roadblocks were then called for the third time, pointing to another test 24 hours later.
This time the test concluded with Elon noting cryo proofing was a success.

Void · 2020-10-23 14:59:06

------
OK, I am very encouraged by what I think is the direction that SpaceX is taking.
I have read an article, which I cannot seem to pull up on this computer, that the SpaceX strategy might be that they will park a starship in LEO, and fill it up and then send a Lunar Starship to it to take on a load. Some reasons I like this.....
Alright, I finally pulled the article up:
https://www.inverse.com/innovation/luna … king-shape
In that method, where nature of orbit is not defined, still it may work well. Using a Starship as a depot, to fuel a Starship specialized for a task, such as the Moon.
Speculative:
If you had a solar unit in orbit that did two things, you could more benefit. If it promoted active cooling, and also ion propulsion, it could be valuable. I don't think Elon Musk or SpaceX is shy about solar, or that SpaceX is shy about solar on Mars. So, solar....
If it is robust enough per thrust of ion engines, it might be able to hover the fuel depot at a LEO level that might not normally be desired. This might allow the Earth Surface <> LEO propellant starships to skimp just a bit on how high they have to go. At the same time if the orbital device, (Solar, Active Cooling, and Ion Drive), were able to then lift the depot Starship to a desired orbit and keep it's propellants from boiling off, you may be where you want to be.
Opportunities suggest themselves. Move the depot from low LEO, to an eliptical orbit, by ion drive, then fuel the mission Starship. Or, you might use a depot Starship as a booster to start sending a mission Starship on it's way. Or you might do both. Cost of course matters, but when you are getting ready to go where no Starship has gone before, maybe a little extra cost, is actually dollar wise. The first objective is to "Do it at all", and that almost certaily does not get you to efficiency.
Efficiency comes later, when you know all the wrinkles of the situation better.
Done.

SpaceNut · 2020-10-23 19:28:52

End of article

"October 2020 – Starship SN8 completes the first triple-Raptor static fire."

The stage from what I remember requires the 3 regular with 3 vacuum compensated to be mounted in the final form or has that changed?

https://www.teslarati.com/spacex-starsh … -schedule/

“passed cryo proof” is sustained pressures of 7.5 bar (~110 psi) or more of which I have seen 8.4 bar for human use is required....

SpaceX has stacked a flightworthy Starship prototype to its full height, leaving just one major step to go before the rocket will be tasked with an unprecedented 15 km (~50,000 ft) flight test.
On October 21st, after much anticipation, SpaceX joined the first flightworthy Starship nosecone with a stack of five structural steel rings, reinforced with longitudinal beams known as stringers. Now, on October 22nd, SpaceX has successfully stacked the rocket to its full height, installing the just-finished nose section to effectively complete the first flightworthy ~50m (~165 ft) tall Starship prototype.

Starship-Boca-Chica-102220-NASASpaceflight-Nomadd-SN8-nose-mate-c-1024x488.jpg

GW Johnson · 2020-10-24 09:29:42

The published numbers for the Starship vehicle as it is currently understood are:
payload 0 to 100+ tons (metric tons)
inert structure 120 tons (goal 100)
max propellant load 1200 tons (main plus small header tanks)

For these numbers the dry-tanks burnout mass is 120-220+ tons, for which the corresponding Earth weights are 1.177-2.157 MN; and the ignition mass is 1320-1420+ tons, for which the Earth weights are 12.945-13.925 MN.

The engine configurations are 3 sea level Raptors, each 2 MN sea level thrust, and 3 vacuum Raptors, which cannot be used at sea level at all! That puts the sea level total thrust of SN-8 at 6.0 MN. It CANNOT takeoff at full propellant load, even at zero payload, because the weight would be at least 12.9 MN, much greater than the available thrust.

Allowing a thrust/weight ratio of 1.10 at ignition, to achieve 0.1 gee net upward acceleration at liftoff (which is VERY sluggish), the available 6 MN of thrust can push no more than 5.455 MN of weight, corresponding to a liftoff mass of no more than 556.2 metric tons. At zero payload, subtracting 120 ton inert gets you the max propellant load of 436.2 metric tons to fly the test. That is 36.35% of the rated max propellant load.

Even if you put 6 sea level raptors in the tail, that's still only 12.0 MN of thrust. At the very sluggish 0.1 gee net upward (thrust/weight = 1.1), the max liftoff weight is 10.909 MN, corresponding to 1112.4 metric tons. Again, at zero payload, the max propellant load is 992.4 metric tons, which is 82.70% of the max rated 1200 tons of propellant.

This vehicle's thrust is too undersized for it to ever be used an an SSTO, or as a point-to-point rocket transport suborbitally. Spacex always intended it to fly atop Superheavy as a TSTO, and even for the suborbital missions. The evidence is right there in the thrust and weight numbers.

It's actually worse, because Musk said in public at Boca Chica they want liftoff thrust/weight = 1.5 to get decent ascent kinematics. I used a crummier T/W figure here, for an early suborbital flight test.

We also need to examine the landing numbers. I've been guessing 15-50 tons of propellant to cover landing. Use 100 tons payload, 120 tons inert. Assume thrust/weight = the operational 1.5 as a minimum to achieve touchdown kinematics at 0.5 gee net upward acceleration capability.

You have 3 sea level Raptors at full thrust for 6.0 MN. At T/W=1.4, the weight is 4.0 MN, and that corresponds to 407.9 metric tons. Note that all three sea level engines MUST be firing to do this. That is NOT wise, you really ought to figure this for one engine out, only two engines at full thrust.

The total of propellant plus payload at touchdown can be no more than 287.9 metric tons (figured at 120 ton inert), for all three engines working. If you are carrying 100 tons payload, that's 187.9 tons max propellant. If you are carrying 200 tons payload, that's 87.9 tons propellant. It's a tradeoff, without a lot of design margin over what I have previously estimated. And, the more payload you carry, the more propellant you must expend to land. The rocket equation tells you that, from the landing effective delta vee figure.

Figured more wisely for 2 working engines, the thrust is 4 MN, the max weight (at T/W = 1.5) is 2.667 MN, corresponding to a touchdown mass of 271.9 metric tons. Subtracting 120 tons inert, the total of payload and remaining propellant at landing cannot exceed 151.9 tons.

If you risk a dry-tanks landing, your max landable payload is 151.9 tons. If you land with 10 tons residual propellant, your max payload is 141.9 tons. If you carry 100 tons payload, your residual propellant after landing cannot exceed 51.9 tons. Etc.

Now do you see why Spacex is currently claiming this vehicle to be capable of "100+ metric tons payload"? It's a landing limitation, as much as anything.

And do you also see why my reverse-engineering numbers for Starship are actually well inside the ballpark?

GW

Last edited by GW Johnson (2020-10-24 09:32:21)

SpaceNut · 2020-10-24 11:58:36

That accounts for the low level of flight heights as its due to fuel levels being used for each as its calculated for the determined response to the engines performance.
Sounds like we can have different engines and count for a given purpose as there is plenty of room to place them in.

SpaceNut · 2020-10-25 15:16:35

The Starship program is unique and one of the most ambitious in the history of rocketry.
The design has now gone through at least twelve known versions and four different names!
Its first version was a single or triple-core rocket back in 2013, which has evolved into the single-core stainless steel Starship design under construction today.
Even as the design’s size has fluctuated dramatically, its repertoire of missions and roles has expanded.

Previous version 11

Version 12 (Starship-May 2020)
The twelfth version of the design saw yet another Starship variant added: a propellant depot ship. The new version began taking shape after Elon Musk confirmed an array of changes to the design on March 16, 2020

More changes for the use for the moon

On April 30, 2020, it was announced that SpaceX had won a $135 million NASA Artemis Program contract for a lunar lander version of Starship. It would dwarf the Apollo LM lunar lander, standing over seven times higher at 50 m (164.0 ft.) vs. 7.0 m (22.9 ft.), with fifty times the crew capacity (100 vs. 2) and over 150 times the pressurized volume (1000+ m3 vs. 6.65 m3). The version could potentially land 100 tons of cargo and eight times more astronauts than walked on the Moon during the entire Apollo Program.
SpaceX’s Artemis related plans call for a LEO Starship flight, a follow-up reflight, propellant transfer between a Starship and tanker, a longer duration orbital Starship mission, and a flight beyond LEO. All of this will precede an uncrewed lunar landing demonstration mission in 2022.

Of course none of this happens until you have the ever changing first stage

In a September 1, 2020 tweet, Musk noted further changes to the engines. The Super Heavy would now only use 28 Raptor engines, three fewer than before. The regular Raptor engines would see thrust upped by 5% from 200 tf to ~210 tf (2,059 kN/ 463,000 lbf), while a new, fixed thrust version would produce 300 tf (2,942 kN/ 661,400 lbf). Eight centrally mounted, variable thrust gimbaling Raptors would help Super Heavy perform directional changes.

SpaceNut · 2020-11-02 22:09:02

As Starships line up, Musk calibrates expectations for SN8 test]

Lifting off under the power of the three Raptors, SN8 will be aiming for an altitude of 50,000 feet. Then, for the first time during Starship testing, the aero surfaces will come into play, as SN8 glides/descends – or, as many like to word it, bellyflops back toward terra firma.

GW Johnson · 2020-11-14 10:17:20

So, they will try the belly-flop maneuver in the first flight after all. Ambitious!

The risk is very high, but I wish them well. Hope they succeed.

GW

louis · 2020-11-14 19:53:52

I prefer the "why should it fail?" approach.

SpaceNut · 2020-11-14 21:48:12

Starship SN8 hoping for speedy return to testing as additional vehicles line up]

The first test involved the first-ever firing of a Raptor engine via the two Header Tanks, one of which – the LOX Header Tank – being located at the nosecone’s tip.
The reasoning for the single, then dual, engine firing relates to the latter part of Starship SN8’s test flight, with the Raptors involved with flipping Starship from horizontal to vertical and then conducting the landing burn.

So engine alignment is critical to make the belly up position happen.

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