Starship is Go...

louis · 2019-09-30 18:43:17

Indeed but there is no "no risk" mission. What's to say if you land a rover (as seems to be NASA's plan) but you find you are sitting over some sort of ice lake which is fine with a one ton Rover but not a 200 ton Starship? I think the cargo ship landing (and subsequent checks - you could use robotic lasers and other instruments in the cargo ships to test the ground) is a reasonable enough safety check.

That said, I still think the orbital satellites are pretty accurate at identifying dense rock...and I can't think of any incident during my lifetime where substantial and dense rock just "collapses". Sink holes don't happen in rocky outcrops. Obviously some rocks are weak and will crack under pressure. But Space X would be looking to land on areas of dense, firm rock and I think that can be id'd from orbit.

SpaceNut wrote:

The issue for sending crew when the chances of cargo ship lose is a no go for safety even if they land whats to say that the crew ship will not have the issue even though the others landed safely....

elderflower · 2019-10-01 03:07:08

GW. Does 7-8 mbar of CO2 count as a vacuum for the purpose of landing a rocket?
Why would Nasa elect to use the novel skycrane arrangement rather than a proven drive off platform, if not to avoid exhaust blasting effects?

tahanson43206 · 2019-10-01 07:08:11

The discussion between GW Johnson and elderflower inspired me to see if there might be a study somewhere, on this subject.

Right off the bat, Mr. Google came up with this! It includes study of Mars for planning for crewed landings.

The paper includes discussion of multiple regimes of behavior of matter under various environmental circumstances.

It opens with a reprise of GW Johnson's advice that landings on one body should NOT be taken as indicative of conditions on another body.

https://sciences.ucf.edu/class/landing- … e-effects/

(th)

GW Johnson · 2019-10-01 08:35:57

To answer the question whether 7-8 mbar is equivalent to vacuum for a rocket exhaust, I used my reverse-engineered data for "Raptor" that is posted over at my "exrocketman" site. Consider that it is the pressure match between the exit plane expanded pressure and the surrounding atmospheric pressure that determines whether the released jet stays collimated or fans out widely. If it fans out widely, it exerts way far less effect upon impact with the surface.

For a "sea level Raptor", I got expansion pressures of 9.18 psia at full chamber pressure of 4400 psia, and 1.84 psia at the 20% throttled point of 880 psia. To translate 7-8 mbar to those units, consider that 1013.25 mbar = 14.696 psia = 1 standard atmosphere of pressure. 7-8 mbar translates to 0.10 to 0.12 psia. There's a huge pressure ratio driving rapid plume fan-out at the exit lip. It's essentially vacuum.

For the "vaccuum Raptor", the expanded pressures are lower for the same chamber pressures. I got 1.22 psia at full thrust 4400 psia chamber, and 0.24 psia at throttled-to-20% 880 psia chamber. For the full thrust exit pressure, there is still a huge pressure ratio causing the plume to fan out. For the min thrust condition, the ratio is only 2. The plume fans out, but not so drastically.

You can also see this in the plots I show on "exrocketman" for thrust coefficient, thrust, and Isp performance vs altitude in Earth's atmosphere. They essentially level out at pretty near vacuum levels at just about 100,000 feet, which is where Earth's air pressure is the same as that at the surface of Mars.

Yep, it's pretty much vacuum on Mars for any practical rocket engine.

GW

Last edited by GW Johnson (2019-10-01 08:37:56)

Oldfart1939 · 2019-10-01 10:49:25

Louis-In my past career as a laboratory and manufacturing chemist, we had a saying: "Theory guides, but experiment DECIDES." What we have from NASA "data," which is in large part--inferential.The only way we are going to get the information regarding landing on surface of Mars is by DOING IT. This is another reason I was sad to see SpaceX abandon the Red Dragon missions to Mars, which would have given real time and hard experimental data about the surface upon which landings will be attempted.

I applaud your undying enthusiasm for all things SpaceX, but temper it with a dose of reasoned skepticism.

GW Johnson · 2019-10-01 11:26:56

I forgot to answer the question about the "Skycrane".

The Curiosity rover was just a bit too big to land the way they did Viking and nearly everything since. As a drive-off type of retropropulsive lander platform, with a 1-ton drive-off rover, their entry aeroshell came out of hypersonics too low to get a parachute out, much less have the time to slow the package from Mach 2.5 (iffy at best for the chute) to transonic (which is the terminal velocity range on Mars, as quite distinct from that on Earth).

So they had to get the weight off without reducing the size. They deleted the usual retro platform in favor of the lighter "Skycrane" concept. That got them a bit higher up at end of hypersonics, so that the ringsail chute could actually do its job. They were really nervous about using "Skycrane", because it had never been done before.

The only other concept they had was the airbag landing. That literally hits the surface at the transonic terminal chute speeds. It worked with the two tiny rovers, but the inevitable square-cube scaling laws WILL NOT let that work with a 1-ton rover! So they were literally forced to do something new.

That quandary, driven by ballistic coefficient during entry in the near-vacuum that is Mars's atmosphere, is EXACTLY what the Justus and Braun EDL and landing report is all about, and in turn THAT is the source of all the extendible and inflatable heat shield concepts that act to reduce ballistic coefficient (if they can be made to really work - that is not yet certain).

GW

Oldfart1939 · 2019-10-01 12:35:14

Just my humble thoughts on what Starship Mk. I can (and WILL) accomplish. GW did the math on the initial acceleration of Starship Mk.I versus total mass of vehicle and projected takeoff thrust available, so a full fuel load seems improbable, but even a 90 % load should allow the vehicle to reach the 20 km mark and perform the pitch-over into the "skydiver" configuration in order to re-land. I suspect that the landing maneuver is what it's designed to do, and not too much more other than test the throttling of the engines in landing. It's sure not going as a SSTO!

louis · 2019-10-01 13:49:59

I thought Sky Crane was more about avoiding have to carry a lot of propellant for a soft retro landing...but maybe I misunderstood things.

elderflower wrote:

GW. Does 7-8 mbar of CO2 count as a vacuum for the purpose of landing a rocket?
Why would Nasa elect to use the novel skycrane arrangement rather than a proven drive off platform, if not to avoid exhaust blasting effects?

louis · 2019-10-01 13:56:38

I'm an enthusiast for Space X because they keep agreeing with me: retro landing, planetary passes, solar power... lol I haven't heard yet whether methane-oxygen will be their preferred method of energy storage, but I'll be happy when they come on side!

Oldfart1939 wrote:

Louis-In my past career as a laboratory and manufacturing chemist, we had a saying: "Theory guides, but experiment DECIDES." What we have from NASA "data," which is in large part--inferential.The only way we are going to get the information regarding landing on surface of Mars is by DOING IT. This is another reason I was sad to see SpaceX abandon the Red Dragon missions to Mars, which would have given real time and hard experimental data about the surface upon which landings will be attempted.
I applaud your undying enthusiasm for all things SpaceX, but temper it with a dose of reasoned skepticism.

SpaceNut · 2019-10-01 16:37:08

louis wrote:

methane-oxygen will be their preferred method of energy storage

At that point we are not coming home if we are not storing it for later use.

Sky crane is a hovering platform by which the crane on the platform lowers the payload aka rover to the ground, releases it and then flys away. The crane lowers the payload to beyond the exhaust so as to get it out of the plume before igniting the engines to hover. That said the skycranes engines are angled outward to aid in the task of directing the exhaust away from the payload.

If we were still going with the Red Dragon the canted super Draco's it would be already in position for direct use with no crane.

GW Johnson · 2019-10-02 11:35:37

With "standard" drive-off landers, you have a base underneath the rover, usually with an instrument platform, and some landing legs. And you have propellant tanks and rocket engines for the touchdown.

With skycrane, you have a much smaller member mounted above the rover that has winches and cables, no instrument platform, and no landing legs. You still have propellant tanks and rockets for the touchdown, but overall it's lighter, and that gets you the end-of-hypersonics altitude required for chute deployment and deceleration to be effective.

Actually, it's pretty simple. But about 1 ton's worth of rover is about it. Square-cube scaling laws won't allow a ballistic coefficient low enough to keep that end-of-hypersonics altitude, beyond about 1 ton. Ballistic coefficient is a prime example of something that really goes by the square-cube scaling laws.

To land anything bigger, you have to either make chute-less retropropulsion work for landing, or you must make extendible heat shields work for a lower ballistic coefficient. At this time, no other option is known. Given what Spacex and Blue Origin have been doing, retropropulsion is farther along technologically.

GW

louis · 2019-10-02 16:15:50

Thanks for the explanation GW. Getting the Skycrane to work on Mars was extremely impressive. It's the sort of thing NASA do well...

GW Johnson wrote:

With "standard" drive-off landers, you have a base underneath the rover, usually with an instrument platform, and some landing legs. And you have propellant tanks and rocket engines for the touchdown.
With skycrane, you have a much smaller member mounted above the rover that has winches and cables, no instrument platform, and no landing legs. You still have propellant tanks and rockets for the touchdown, but overall it's lighter, and that gets you the end-of-hypersonics altitude required for chute deployment and deceleration to be effective.
Actually, it's pretty simple. But about 1 ton's worth of rover is about it. Square-cube scaling laws won't allow a ballistic coefficient low enough to keep that end-of-hypersonics altitude, beyond about 1 ton. Ballistic coefficient is a prime example of something that really goes by the square-cube scaling laws.
To land anything bigger, you have to either make chute-less retropropulsion work for landing, or you must make extendible heat shields work for a lower ballistic coefficient. At this time, no other option is known. Given what Spacex and Blue Origin have been doing, retropropulsion is farther along technologically.
GW

SpaceNut · 2019-10-06 17:58:23

MK1 prototype to get

https://www.teslarati.com/spacex-starsh … s-spotted/
https://www.nextbigfuture.com/2019/09/s … entry.html

Same batteries that burst into flame and total your car to power starship is not such a good idea...

GW Johnson · 2019-10-07 07:46:52

There is a lithium battery technology that does not flare up into flame, and survives puncture or other severe damage without that danger. It has a solid electrolyte in powder form. But this is a garage-scale startup. It has not been industrialized/scaled-up for application. Too many established competitors already out there (who do catch fire).

GW

louis · 2019-10-09 07:52:33

Possible that construction of Mk 3 at Boca Chica has already started...

https://www.youtube.com/watch?v=L0qM5MXxd6w

louis · 2019-10-14 13:19:01

It's Felix time!

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

Another good video from Felix's oddly named "What About It?" channel.

Mark 4 construction might have begun (one ring laid down).

SpaceNut · 2019-10-14 21:02:06

https://www.spacex.com/starship
https://en.wikipedia.org/wiki/SpaceX_Starship

No solar panels or kw ratings for them...
No life support numbers for a crew of 100
No cargo manafest to support the crews food or water needs

So far all we have is the ability to get to mars to land once refueled in orbit, raptor engines and wing battery packs

https://www.cnn.com/2019/09/27/business … index.html

The company is pouring substantial time and resources into the building the hardware it needs to reach Mars,an enterprise that Musk has said could cost between $2 billion and $10 billion. SpaceX would look to create technology that could bring the price of Mars travel to about $200,000 per person, Musk said, down from the $10 billion he estimated it would cost using currently available technology.

getting a ticket down to 200,000 is good news for those wanting to go,

louis · 2019-10-15 17:13:38

Nice it has its own official page now!

Over 380 feet tall! Insanely huge - taller than Saturn V by 20 feet or so.

SpaceNut wrote:

https://www.spacex.com/starship
https://en.wikipedia.org/wiki/SpaceX_Starship
https://www.spacex.com/sites/spacex/fil … p_uses.jpg
No solar panels or kw ratings for them...
No life support numbers for a crew of 100
No cargo manafest to support the crews food or water needs
So far all we have is the ability to get to mars to land once refueled in orbit, raptor engines and wing battery packs
https://www.cnn.com/2019/09/27/business … index.html
The company is pouring substantial time and resources into the building the hardware it needs to reach Mars,an enterprise that Musk has said could cost between $2 billion and $10 billion. SpaceX would look to create technology that could bring the price of Mars travel to about $200,000 per person, Musk said, down from the $10 billion he estimated it would cost using currently available technology.
getting a ticket down to 200,000 is good news for those wanting to go,

louis · 2019-10-17 16:54:08

New Mars Forums

Announcement

#376 2019-09-30 18:43:17

Re: Starship is Go...

#377 2019-10-01 03:07:08

Re: Starship is Go...

#378 2019-10-01 07:08:11

Re: Starship is Go...

#379 2019-10-01 08:35:57

Re: Starship is Go...

#380 2019-10-01 10:49:25

Re: Starship is Go...

#381 2019-10-01 11:26:56

Re: Starship is Go...

#382 2019-10-01 12:35:14

Re: Starship is Go...

#383 2019-10-01 13:49:59

Re: Starship is Go...

#384 2019-10-01 13:56:38

Re: Starship is Go...

#385 2019-10-01 16:37:08

Re: Starship is Go...

#386 2019-10-02 11:35:37

Re: Starship is Go...

#387 2019-10-02 16:15:50

Re: Starship is Go...

#388 2019-10-06 17:58:23

Re: Starship is Go...

#389 2019-10-07 07:46:52

Re: Starship is Go...

#390 2019-10-09 07:52:33

Re: Starship is Go...

#391 2019-10-14 13:19:01

Re: Starship is Go...

#392 2019-10-14 21:02:06

Re: Starship is Go...

#393 2019-10-15 17:13:38

Re: Starship is Go...

#394 2019-10-17 16:54:08

Re: Starship is Go...

#395 2019-10-21 10:40:08

Re: Starship is Go...

#396 2019-10-21 14:37:15

Re: Starship is Go...

#397 2019-10-21 16:25:45

Re: Starship is Go...

#398 2019-10-21 18:04:21

Re: Starship is Go...

#399 2019-10-21 18:26:45

Re: Starship is Go...

#400 2019-10-21 18:29:23

Re: Starship is Go...

Board footer