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#1 Re: Human missions » Why Artemis is “better” than Apollo. » Yesterday 16:25:38
The idea Artemis is “better” than Apollo on cost grounds comes from this assessment of Apollo’s costs in inflation-adjusted dollars:
How much did the Apollo program cost?
https://www.planetary.org/space-policy/cost-of-apollo
The max expenditure in a single year was ca. $45 billion in 2020 dollars. And the total cost of the lunar lander alone was ca. $20 billion in 2020 dollars.
But how much cheaper Artemis is than Apollo exemplifies another key advantage we have now over Apollo that we must make use of: the plentiful commercial launchers, in-space stages, and spacecraft already operational and in regular use.
Then USE that advantage. Construct your lander, small like Apollos, from EXISTING components, not developing the lander from scratch. Knowledgeable observers of the space program are aware of the fact development costs for entirely new systems from scratch incur ballooning costs.
There are multiple ways of following this approach.
Here’s one:
Possibilities for a single launch architecture of the Artemis missions, Page 3: Saving the lander mission for Artemis III.
https://exoscientist.blogspot.com/2023/ … ch_11.html
Bob Clark
#2 Re: Human missions » Why Artemis is “better” than Apollo. » Yesterday 15:10:54
For RGClark...
The post by Mars_B4_Moon comes across to me as having little (if anything) to do with your theme.
It seems to me it is another (rather long) argument that supports the idea that it might be wiser for the human race to try to reach Mars without having proven it's ability to land and live on the Moon.
If you have the time, and it the question is of interest, please review the post by Mars_B4_Moon to see if it has anything to do with the topic you introduced.
For all ... it seems to me there are very few reasons why Artemis might be "better" than Apollo, and RGClark had to really stretch to find one or two.
The list of reasons why Artemis is inferior to Apollo is probably much longer, and Mars_B4_Moon seems to have found several of them.
The key reason for the failure of Artemis was given in the post by Mars_B4_Moon .... the budget for the venture has been severely constrained. NASA leadership has had to try to complete a very difficult mission with a tight budget and without the fever pitch of National enthusiasm that Apollo enjoyed.
Best wishes for success with this topic.... you'll need it!
(th)
He thinks Artemis is unsustainable and will be cancelled. There are some high ticket items still upcoming in the pipeline. The landers still need to be paid for, then the larger Boeing EUS upper stage, then the advanced carbon fiber side boosters, then NASA still wants to build the Gateway. I can’t argue that Artemis is not expensive but looking at the inflation-adjusted dollars it is cheaper than Apollo.
But there is a commercial space approach to cutting the costs of the lander. In commercial space, the development costs are privately funded. This is what I have been arguing for in regards to the lander. Then no billions to SpaceX or Blue Origin for their landers. Following this approach the Gateway is also no longer needed, so those billions are cut. And under this approach lander missions can be done also without the advanced carbon fiber SRB’s so those billions are cut.
There is the issue of the Boeing EUS, though. It would be great if NASA would use the Ariane 5/6 core for the purpose instead. That would increase the payload capacity and save development cost. Then those billions would be cut. But the opinion is it appears politically untenable to give this American contract to a European company instead.
Still, even if we have to retain the Boeing EUS, we can get significant cost savings by using a small, Apollo-sized, commercial, i.e., privately-financed, lander.
Bob Clark
#3 Human missions » Why Artemis is “better” than Apollo. » Yesterday 00:42:51
- RGClark
- Replies: 6
The major problem with NASA implementing Artemis to land on the Moon can be summed up in one sentence: they are still thinking of Artemis as like the Constellation program being “Apollo on steroids”. No, Constellation was much larger with a much larger launcher in the Ares V with plus an additional, separate launcher in the Ares I to get Orion to orbit. No, the correct way of thinking of Artemis is as comparable to Apollo in the sense of the size of its payload capacity and the fact the SLS also has to be used to get the Orion capsule to orbit. And actually on cost grounds you can consider it “better” than Apollo since it is CHEAPER than Apollo since in inflation adjusted dollars it’s about a quarter the program cost.
So, the problem is that in still thinking in “Apollo on Steroid” terms, the idea is retained the lander has to be these humongous landers like the Starship HLS or even the over-large Blue Origin lander. No, just think of the lander as being Apollo size, at ca. 13 ton gross mass of the Apollo LEM.
The right size for an Artemis lander(the one on the right.)
(Image credit Ken Kirtland.)
Then the lander doesn’t have to be some $10 to $20 billion development cost. It can be done for just a few hundred million dollars because the needed propulsive stage(s) and crew capsule already exist. You just have to ask our European partners for those components that already exist and are in operational status.
But the desire is to get Artemis to serve as the launcher for a continually occupied Moon base, a la how the ISS is for LEO. This is actually another sense of how Artemis, or more accurately the current space program in general, is “better” than Apollo. Back in the Apollo era NASA had to develop all the various launchers and stages and spacecraft from scratch, at great expense. But now, don’t think of the SLS or any of the over-large proposed landers to carry cargo to the Moon. Think of any of the several commercial orbital launchers for the purpose. The surprising conclusion you draw is that instead of using the $2 billion per launch SLS for cargo delivery at, at best, a once per year cadence, you can launch cargo to the Moon for costs at about the same as what we spend now to send cargo to the ISS, in the $100 million per launch range and on a weekly basis, by using commercial launchers and small, already existing stages as the landers.
See:
Possibilities for a single launch architecture of the Artemis missions.
https://exoscientist.blogspot.com/2022/ … aunch.html
Bob Clark
#4 Re: Unmanned probes » Low cost Mars Sample Return. » 2024-05-07 16:23:23
Robert Zubrin proposes another low cost approach to Mars Sample Return:
A practical approach to the Mars Sample Return mission
Robert Zubrin
May 6, 2024
https://spacenews.com/practical-approac … n-mission/
This looks also like it could be something done for less than $100 million by commercial space, 1/100th the cost estimated by NASA doing it.
Bob Clark
#5 Interplanetary transportation » Radian Aerospace spaceplane. » 2024-05-03 12:13:31
- RGClark
- Replies: 1
I enjoyed seeing the interview of Radian Aerospace co-founder Livingston Holder. He discusses why their sled-launched spaceplane is technically and financially feasible.
However, the horizontal launch method they propose has the disadvantage of needing heavy wings to support the fully-fueled weight of the spaceplane. In contrast a vertical launch method would use wings that only had to support the dry mass of the craft on return, resulting in much lighter wing weight. I advise Radian to do the trades to find which is the optimal method.
Additionally, I advise they base the core of their vehicle on existing upper stages to save on development costs and technical risk. I discuss using the Falcon 9 upper stage or Centaur upper stage for the purpose here:
Radian Aerospace spaceplane.
https://exoscientist.blogspot.com/2024/ … plane.html
Robert Clark
#6 Re: Human missions » NASA may alter Artemis III to have no Starship landings. » 2024-05-03 10:54:54
From today's issue of "The Daily Launch", AIAA's newsletter:
-------
...
Many of us have already guessed why the Artemis I heat shield misbehaved vs expectations: they removed the hex to make it cheaper to build, and so lost the composite strengthening effect of that hex upon the char layer of the Avcoat polymer. Test data always (ALWAYS!!!) trumps computer code predictions.And if this did not show up in the ground arc jet tests, then they did not run the right tests. It is the sideways fluid shearing force scrubbing at the heat shield that strips poorly-supported char off in chunks. Happens all the time in solid rockets, and especially in subsonic combustion ramjets. Been there and done that, for many years.
Just in case you haven't kept up, the first Orion flight test was not classified as an Artemis mission. That one flew the Apollo-type Avcoat-in-hex heat shield, and it performed just fine, and exactly as expected. The second Orion test flight was Artemis I, with the no-hex variant of the Avcoat heat shield that eroded both erratically geometrically, and on-average significantly faster than expected, although not quite enough to truly endanger the capsule. They had already installed one of these no-hex Avcoat heat shields on the Artemis II/third Orion, before actually testing it on Artemis I (the second Orion).
...
GW
Since this is a safety issue is there a way to communicate to high level managers directly your concerns?
Bob Clark
#7 Re: Unmanned probes » Low cost Mars Sample Return. » 2024-04-23 11:36:40
NASA is now opening up the Mars Sample Return mission to the commercial space approach. The usual NASA government financed approach is estimated to cost ~$10 Billion. But following the commercial space approach it probably could be done at literally 1/100th that at ~$100 million including launch cost.
I had estimated it as less than ~$200 million using the Falcon Heavy as launcher:
Low cost commercial Mars Sample Return.
http://exoscientist.blogspot.com/2023/0 … eturn.html
This could get ~750 kg back from Mars with the Falcon Heavy as the launcher. However, it probably could in fact be launched on the Falcon 9. The Falcon 9 can launch about a quarter of the mass of the Falcon Heavy to Mars, for all the in-space stages, so estimate the sample size returned from Mars of ca. 180kg.
At a $40 launch cost of the reused F9, then all together with all the in-space stages, the mission cost probably could be less than than ~$100 million. Such a low mission cost probably could be paid for by advertising alone.
But to encourage participants to take up the task of such a fully privately financed mission, NASA could offer a prize of say $200 to $500 million to whoever could accomplish it, with some smaller incentive prizes to those who accomplish some key required steps.
Bob Clark
#8 Human missions » NASA may alter Artemis III to have no Starship landings. » 2024-04-21 17:01:00
- RGClark
- Replies: 10
NASA may alter Artemis III to have Starship and Orion dock in low-Earth orbit
If it were to happen, a revised Artemis III mission could echo Apollo 9.
ERIC BERGER - 4/19/2024, 11:20 AM
https://arstechnica.com/space/2024/04/n … rth-orbit/
Note the missions proposed wouldn’t even use refuelings for Starship.
I’m suggesting the reason why NASA is proposing this now is because of the low 40 to 50 ton payload capability for the current Starship Elon announced, a number too low to perform the refueling missions of Starship:
Starship Faces Performance Shortfall for Lunar Missions
by Alex Longo
https://www.americaspace.com/2024/04/20 … -missions/
Bob Clark
#9 Re: Human missions » Long duration Human space missions - Can we survive them? » 2024-04-19 01:44:58
There's a whole lot more to microgravity diseases than just bone loss and muscle weakening from lack of use. That's all that was expected back in the Mercury/Gemini/Apollo days.
We have since found that there is damage to the eyes, there is damage to the immune system, there is damage to the chromosomes (although how much is microgravity and how much is radiation exposure is arguable), and there is damage to the heart and circulatory system. All of these are "for sure" now.
There is as yet no end in sight to this list. As the years go by, we keep finding more and more things in the body that zero gee damages. That trend suggests we do not yet know all the risks.
Each and every one of those things, and a lot of other practical issues about living in space (like how to take a bath, or how to use a familiar toilet, or how to cook on a stovetop), are solved if you add in artificial gravity (as spin). Gees ~ (spin radius/56 m)*(spin rate/4 rpm)^2. There is a max spin rate for long-term exposures: about 3-4 rpm. And THAT means you must use a spin radius equal to or exceeding 56 m! Cable-connected modules, and building Battlestar-Galacticas, are not the only ways to do that, by the way! Although some never bother to think outside those 2 boxes.
The radiation threat is NOT the cosmic ray bugaboo that so many claim! If you hear somebody still claiming that, know that it is BS. Period! At least in the inner solar system, the real lethal threat is big solar flares. The data that we have suggests that 25 g/cm^2 of low molecular weight shielding material would protect well enough, against even a really big solar flare like the 1972 event that occurred between two Apollo missions. Had a crew been out there during that event, they would have died within less than 10 hours, and it is a very ugly death.
Living space is a problem, ask anybody who ever served time in solitary confinement. But it's not just a volume per person. You have different needs at different times.
Sometimes you need to be with other people, sometimes you need to get completely away from other people, and there's a spectrum all in between those two extremes. Shipboard conditions and facilities are a guide to this, but they are simply not "right" for a spacecraft.
On a ship, you can go out on deck and feel the sun and the wind on your face. You cannot do that on a spacecraft, so you will need more spaces and facilities than a ship has. You can't do that "go out on deck" thing on a submarine, but not everybody can be a submariner.
Real life is complicated and messy.
GW
Thanks for that. This video shows why it is important to have some form of artificial gravity for a 6 month flight to Mars:
NASA astronaut shows how hard walking is after return from International Space Station (ISS).
https://www.youtube.com/watch?v=BVHqnXjhuN8
This video shows some proposed means of doing it:
Artificial Gravity is Critical for Mars Exploration & Beyond - SpaceX Starship can make this happen!
https://m.youtube.com/watch?v=he2thPRcpQc
About the radiation shielding issue, 25 g/cm^2 is probably doable for a small habitat for, say, a four astronaut exploration team. But it would require a huge additional mass for a passenger cabin the size of the Starships carrying 100 Mars colonists with 1,000 cubic meters volume.
To estimate it for the Starship, approximate the Starship passenger cabin as a 10m*10m*10m cube. Then that’s 6*10*10 = 600 square meters. An areal density for the shielding of 25 g/cm^2 equals 250 kg/m^2. So a total of 150,000 kg, 150 tons. This is about the mass of the entire payload capacity of the Starship.
For an exhaustive look at the problems of zero gravity and space radiation on long space missions see this book by Dennis Chamberland, a Ph.D scientist who worked 30 years in the biology division for NASA:
Departing Earth Forever: Book One - Warning and Promise: The Manual for Today's Colonists Preparing to Launch to Mars and our Moon Kindle Edition.
https://www.amazon.com/Departing-Earth- … 949&sr=8-1
Bob Clark
#10 Re: Meta New Mars » OldFart1939 Postings and YouTube Video Presentation(s) » 2024-04-19 01:22:09
The Zoom session is set up for the presentation by Dr. Jim Bell
GW Johnson is already in the audience.
Postcards from Mars
NASA's Perseverance Rover and the Dawn of Mars Sample Return
Professor Jim Bell
Arizona State University School of Earth & Space Exploration
Principal Investigator, NASA Mars 2020 mission Mastcam-Z imaging investigation
Past President, the Planetary SocietyOldFart1939 is introducing Jim Bell >> Warm Montana welcome ... It's about 70 today
OH Good! Recording in progress ... hopefully the video will be made available for NewMars members who cannot attend live.
47 robotics missions to Mars since 1960's ... 8 nations ... 10 successful landers
Really difficult destination ... reasons given
About half of the missions have failed ... NASA has 9 successes and China 1
*** Continuing after save
Mars today ... a pretty harsh place ...
Slides were not showing ... Dr. Bell will review ... The slides are not advancing properly
Slide ... 47 missions ....
Next slide ... Mars today ...
Next slide ... Perseverance and Ingenuity
Next slide with videos of rovers
Next slide ... video of Perseverance moving slowly but accurately...
*** Continuing after save
Slide: Mars 2020 Rover Science Payload
Slide: Mars 2020: Jezero Crater ... hard to decide where to go
A lake there a long time ago ... delta like the end of the Mississippi river
Slide:Marsw 2020 Mission Objectives
Geologic Exploration, Habitability and Biosignatures, Prepare a Returnable Cache, Prepare for Human Exploration
Note last item: Demonstrate in Situ Resource Utilization by converting atmospheric CO2 to O2
Note that Dr. Bell thinks that Chinese explorers might be first, in addition to NASA and SpaceX
Slide: Mars 2020 Mission Timeline
Very difficult because of global pandemic ... all possible protections for workers on site
Sol 1119 is today for the lander, on site!
Video ... Perseverance lands on Mars ... combination of animation and live pictures
Nice video!
*** Resuming after save
Slide ... landed close to where we wanted to go .... praise for rocket scientists and engineers
Slide ... https://mars.nasa.gov/mars2020/mission/ … the-rover/
Slide ... detail of travel plan
Slide landing site
surface flat by intention ...
Slide Sol 4 checkout - surround view - ? 360 degrees ?
Slide ... Martian Delta ... slide 18 Enormous boulders
Slide... helicopter ... tucked under the rover when landed
April 30th of 2021 ... spun blades for the first time
2500 rpm ... note that videos are embedded in the slide
A tiny patch from the Wright Brother's flyer is on the helicopter
Video from helicopter ... Ended up taking 72 flights ... far beyond mission goal
A mission has been approved ... Dragonfly ... quadcopter...
Slide ... first drilling / Coring attempt
Core tube came up empty... Rock too soft and crumbly
Slide ... hard volcanic rock nearby ...
Slide... view of end of corer ... numerous samples are visible in the slide
4 and a half billion years .... volcanic rock overlaid the floor of the lake
Slide ... Dusty place ... little video of dust devels dirt on rover at sols 286 to 321
Slide ... Delta bound ... sand dunes ...
Slide ... samples of layered rocks
Slide ... samples ... October 2022 ... Sedimentary Mudstone
Arrived at delta front in late 2021...
Slide 28 ... Second delta core samples in the can October 2022
Slide 29 ... Hunting for Regolith!
Slide 30 ... trail of movement ... Depot the Backup Cache ... dropped off 10 sample tubes in a little parking lot
Slide 32 ... depot
Slide 34 ... Pinestand Mountain Sol 718
Slide 35 Skrinkle Haven
Slide 36 Filling all the tubes ... 24 samples so far
Slide 37 ... Phobos solar eclipse
Used the image astronomically to determine the orbit of Phobos
Another part of this slide ... Mastcam-Z Sol 1039
Slide 38 ... 72nd flight of Ingenuity .. Jan 19, 2024 ... ... rover lost it's orientation due to sandy surface
Some day there may be a Smithsonian on Mars ... historic aircraft
Slide 39 ... Tough Driving
Slide 40 ... more samples.... 21 rock cores, 2 soil samples , 1 atmospheric sample, 3 "witness tubes"
Slide 41 ... landscape
Slide 42 .... 24 Samples in the Cache ... "witness" tubes will be left empty to check whether there was contamination from Earth
https://mars-rock-samples at Nasa web site
Slide 43 ... Mars Sample Return ... mission not yet funded
*** continuing after save ...
Discussion of funding challenges ... Congress decided the original plan was too expensive ... 10 billion dollars
Comparable to James Webb telescope
Monday there will be a NASA press conference to announce a new plan
Video ... Mars Sample Return ...
Slide 45 ... description of global scientific analysis of samples
Slide 46... back to Mars Exploration Family Portrait
77 space agencies around the World now!
Slide 47... Follow along
http://mars.jpl.nasa.gov/mars2020
Question ... how long to take a sample?
Very slow process ... Tai Chi dance the engineers have to perform to move the samples.
There is a second robotic arm to stow the sample
Question: ... can the rover pickup samples ? No... the rover cannot do that
A new rover is needed to pick up the samples
Question ... what are the black parts of the pictures ... those are landscapes assembled from multiple pictures.
Question about slide 35 ... the black section is the rover itself ... it is expensive to send data.
Question: ... missed the question ... answer "I don't know"
Possibly it was how long will the equipment last ... ? 80 years ?
A greater concern is funding ... NASA's budget has to pay for keeping these missions going.
The equipment may well outlast funding....
Next: Two books .... 2006 ... started writing books
*** continuing after save
Art of the Cosmos... another picture book
Not sure which book this is ... covers the geological history of our planet ...
wrote a book about space in general ...
? book about Voyager .... narrative book
First Saturday in May ... next meeting
Quite an interesting list of topics. Anyway to see it recorded on Zoom or YouTube?
Bob Clark
#11 Interplanetary transportation » A route to aircraft-like reusability for rocket engines. » 2024-04-18 12:05:07
- RGClark
- Replies: 2
A route to aircraft-like reusability for rocket engines.
https://exoscientist.blogspot.com/2024/ … ility.html
An interesting discussion on longevity of jet engines:
The question I raise is whether this could also increase the reuse capability of rocket engines.
Near the end I suggest, SpaceX is using this principle of running the engines at lowered power to increase engine life for the purpose of increasing the reliability of the Raptors. If they are, then they should explore the potential of this principle to also extend rocket engine reuse capability.
Bob Clark
#12 Re: Human missions » Starship is Go... » 2024-04-14 23:52:39
A key issue now is I think NASA was blindsided by the low value of 40 to 50 tons payload capacity of the current version of Starship. The reason I think that is if you run the numbers for the SpaceX cited specifications for booster and ship dry and propellant mass, and for Raptor thrust and ISP the vehicle should easily make 100+ tons payload even as reusable.
So what accounts for the lower payload capacity for the current version? Either the dry mass values or the Raptor values or both must be significantly worse than those cited by SpaceX.
Bob Clark
#13 Re: Human missions » Starship is Go... » 2024-04-11 10:38:43
SpaceX should withdraw its application for the Starship as an Artemis lunar lander, Page 3: Starship has radically reduced capability than promised.
https://exoscientist.blogspot.com/2024/ … ation.html
Robert Clark
#14 Re: Human missions » Starship is Go... » 2024-04-08 13:57:25
The full video is here:
Elon Musk Starship Presentation: IFT-4 Master Plan, Starship V2 & V3, Raptor V3, Mars, IFT-3 & More.
https://youtu.be/z3B0XIImf_w
About 31 minutes in Elon suggests the current version V1 would be capable of 40 to 50 tons to orbit. This is bad because SpaceX sold NASA on the idea the Starship HLS could serve as an Artemis lander based on 150 tons to orbit reusable and “10ish” refueling flights. If the capability is max 50 tons, then it would take “30ish” refueling flights.
If they intend to use version V2 then this is bad because it would require further qualification flights for the larger version and more importantly further qualification of the more powerful Raptor 3 engine needed.
This last is doubly bad because I’d be willing to bet dollars to donuts that they never informed NASA that the current version couldn’t do it and further development would be required for the larger version.
Bob Clark
#15 Re: Human missions » Starship is Go... » 2024-04-01 23:24:49
So what changes did SpaceX make to insure Starship didn’t reach orbit when Elon said before the flight it had a 80% chance of reaching orbit?
“Starship Flight 3 Update - Probability of Reaching Orbit 80%” said Elon Musk.
https://www.youtube.com/watch?v=lCe8a7XcG8o
Oddly, not only did he say before the flight Starship had an 80% chance of reaching orbit, he even said on Twitter after the flight it did reach orbit:
Elon Musk @elonmusk
Starship reached orbital velocity!
Congratulations @SpaceX team!!
9:40 AM · Mar 14, 2024 45.5M Views
6.9K 16K 209K 1.6K
https://twitter.com/elonmusk/status/1768271078999167379
An odd thing for the Chief Engineer of SpaceX to say. This tweet from Elon received 45 million views. Apparently, it led many news sources to repeat the claim Starship reached orbit on IFT-3:
RESEARCH
Payload Research: Tracking Starship’s Progress with Additional Flights on the Horizon
By Jack Kuhr
March 20, 2024
Starship reached orbital velocity during IFT-3 last week, largely validating its capability as an expendable rocket while SpaceX continues to try to nail down vehicle recovery.
https://payloadspace.com/payload-resear … iguration/
Bob Clark
#16 Re: Meta New Mars » GW Johnson Postings and @Exrocketman1 YouTube videos » 2024-03-30 11:46:42
…
As for 150 tons vs 1 ton, a gross estimate would be (100 kg/sq.m)*cube root of (150 ton/1 ton) = 531 kg/sq.m. That'll come out of hypersonics somewhere down near 5 km at 0.7 km/s, just like Starship. On the slant, you have about 7 km path length, to cover at the average of 0.7 km/s and 0 km/s, for about 20 sec to decelerated touchdown. That's an average deceleration of 700 m/s in 20 sec, or 35 m/s2. Or a tad over 3.5 gees! It's doable! But a rough ride, especially for people exposed to microgravity for multiple months getting there.GW
So perhaps about 0.7km/s that needs to be cancelled out by rockets for a 150 ton lander. Even if the higher estimate of 1.1 km/s is needed, that’s not particularly difficult. I wonder why NASA considered landing large, crewed habitats on Mars such a daunting problem:
The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet.
POSTED ON JULY 17, 2007 BY NANCY ATKINSON
Some proponents of human missions to Mars say we have the technology today to send people to the Red Planet. But do we? Rob Manning of the Jet Propulsion Laboratory discusses the intricacies of entry, descent and landing and what needs to be done to make humans on Mars a reality.
There’s no comfort in the statistics for missions to Mars. To date over 60% of the missions have failed. The scientists and engineers of these undertakings use phrases like “Six Minutes of Terror,” and “The Great Galactic Ghoul” to illustrate their experiences, evidence of the anxiety that’s evoked by sending a robotic spacecraft to Mars — even among those who have devoted their careers to the task. But mention sending a human mission to land on the Red Planet, with payloads several factors larger than an unmanned spacecraft and the trepidation among that same group grows even larger. Why?
Nobody knows how to do it.
https://www.universetoday.com/7024/the- … ed-planet/
Bob Clark
#17 Re: Meta New Mars » GW Johnson Postings and @Exrocketman1 YouTube videos » 2024-03-30 07:10:40
…
THAT is what it all boils down to: getting to the surface! Because THAT SURFACE is where the resources are, and THAT is where propellant and life support supplies will be manufactured! And that surface is where people have dreamed of going for some centuries now. Better to just belly up to the bar and simply do it right!GW
Are you saying you can land a 150ton crew module on Mars? That would be about the size of the SpaceX Starship with provisions. What would be the size of the parachutes? What would be the speed needed to be cancelled out by propulsion? How much propellant would that take?
Bob Clark
#18 Re: Human missions » Starship is Go... » 2024-03-30 00:03:48
How do we know that SpaceX did not throttle the engines in such a way as to account for not having any payload aboard?
I think you have to do that to some degree, in order to remain within airframe structural limits. Any throttling of the engines makes them less fuel efficient than they are at maximum thrust, same as with any other gas turbine based engine technology. You burn a lot more fuel at lower power settings, relative to the thrust being generated, but that is not the same as not having thrust available. That doesn't automatically mean an unladen Starship struggles to achieve orbit, merely that running the engines at lower thrust than nominal, happens to be a great way to "burn" a full propellant load without achieving maximum possible thrust. They're shoving all the propellant mass through the engines, proving that all the mass will go through the engines without the engines exploding. If you don't throttle up all the way, then in the same way that a low-bypass turbofan or turbojet eats fuel like mad at idle power, while producing negligible thrust, I'd imagine that a rocket could be run in a similarly inefficient manner. The upside is that this avoids bending things on a very lightly loaded upper stage. This thrust manipulation is done with virtually all liquid fueled rockets to maintain acceleration rates and avoid over-stressing the airframe, so I see no reason why Starship cannot do the same thing.
Perhaps, GW can address this but I can only think of three ways a rocket in general can launch a smaller payload than what its max payload capability is. Note, usually a rocket carries much less payload than it’s max capability. For instance the Falcon 9 has 22.8 ton max payload to orbit but it never launches that much.
One way is to partially fuel the rocket, another way is to cut the stage burns early, a third way is to throttle down the engines. This video shows essentially full propellant loads at launch for both stages and essentially full propellant depletion at stage shut down:
FULL FLIGHT! SpaceX Starship IFT-3.
https://youtu.be/W1WfCVZFZPo
If the burns were shut down early then you would have more left over propellant. That didn’t happen. So the third way is to throttle down the engines. I have speculated that SpaceX has done this:
Did SpaceX throttle down the booster engines on the IFT-2 test launch to prevent engine failures?
http://exoscientist.blogspot.com/2023/1 … oster.html
The problem is SpaceX won’t admit it has done this. This is an important point because my argument is that SpaceX throttles down the engines to increase engine reliability, and SpaceX won’t admit there is still a problem with engine reliability.
If SpaceX is throttling down the engines just because of smaller payload, why not just admit that? Why this pretense of running the engines at full power?
Bob Clark
#19 Re: Human missions » Starship is Go... » 2024-03-29 09:22:49
For RGClark re #1785
My understanding is that the flight plan was NOT intended to reach orbit.
Instead, it has been announced for months that the plan was to drop the second stage in the ocean.
The question that might be useful to know, if there is any way of finding the data, is how much mass was left in the Starship tanks at engine cutoff.
The answer to the question you posed (about delivery capability) might derive from that knowledge.
It will take some research to find the answer, and it may not be published or available indirectly, but I'm hoping you have the energy and the interest to see if you can find the answer and post it here.
(th)
Yes, the planned trajectory was to be just short of orbit. But that speaks even worse for SpaceX because it means IFT-3 demonstrated a vehicle with negative payload to orbit capability even though fully fueled and fully expending propellant.
You can see the propellant load of both stages in the graphics overlain by SpaceX on the launch video, showing the both stages virtually fully loaded with propellant on launch and virtually fully expended on engine shutdown:
FULL FLIGHT! SpaceX Starship IFT-3.
https://youtu.be/W1WfCVZFZPo
Bob Clark
#20 Re: Human missions » Starship is Go... » 2024-03-29 01:57:51
Elon Musk @elonmusk
Getting ready for Flight 4 of Starship!
Goal of this mission is for Starship to get through max reentry heating with all systems functioning.
https://x.com/elonmusk/status/1773085211275698302?s=20
How about showing it can get anywhere near the 150 tons payload to LEO claimed?
What IFT-3 showed was a launcher with 0 tons to LEO payload capability, even when fully fueled and fully expending its propellant. Then how can it do Artemis Starship HLS refuelings when it gets 0 tons to LEO?
Bob Clark
#21 Re: Human missions » Starship is Go... » 2024-03-26 22:23:59
SpaceX said they performed a “full duration” static fire of the Starship:
SpaceX @SpaceX
Full-duration static fire of all six Raptor engines on Flight 4 Starship
https://x.com/SpaceX/status/1772372482214801754?s=20
Sorry, but no. A 10-second burn is not full duration. THIS is full duration:
Another irritation of mine is that SpaceX won’t tell you what power level their tests are operating at. 50%?, 75%?, 100%? Usually, the launch company tells you this in their tests to confirm to potential customers their engines can operate at the needed power levels to complete their missions.
Robert Clark
#22 Re: Human missions » Starship is Go... » 2024-03-26 22:08:17
Marcus House speculates in response to a question from one of his viewers that the reason the SH/SS just barely made orbit on IFT-3 when it had 0 payload that perhaps it was only partially fueled. See at the 5:18 point here:
SpaceX's Frantic Push to Launch the Next Starship Mission is Nuts!
https://youtu.be/1HAcza0nE34
But actually SpaceX prior to the IFT-3 launch said SH/SS was fully fueled:
SpaceX @SpaceX
Propellant loading complete. Starship is fully loaded with more than 4500 metric tons (or 10 million pounds) of propellant
9:22 AM · Mar 14, 2024
https://twitter.com/SpaceX/status/1768266565085266349
Then the question remains: when payload capability is supposed to be 100-150 tons, why does a fully fueled SuperHeavy/Starship just barely make orbit(actually slightly less) carrying no payload, fully expending its propellant?
Think of it this way, what SpaceX demonstrated with IFT-3 was a launcher with a payload to LEO capability of 0 tons even when fully fueled and fully expending its propellant. Then how can it do Artemis Starship HLS refuelings when it gets 0 tons to LEO?
Bob Clark
#23 Re: Human missions » Starship is Go... » 2024-03-26 21:49:41
Stainless steel never approaches the tensile strength of carbon fiber, regardless of temperature. I keep hearing this nonsense spouted off as if it were a fact. It is objectively and provably false.
…
Toray standard modulus carbon fiber yields / fails at 415ksi. Their T700 high modulus carbon fiber yields / fails at 710ksi. T800 yields / fails around 852ksi. Some of the strongest steels available, none of which are suitable for cryogenic temperatures, yield between 350ksi and 400ksi. There is no metal alloy that I'm aware of that yields at 700ksi. I'm just shy of absolutely certain that no metal alloys yield at 852ksi, and any that did would be unsuitable for propellant tanks subjected to both tensile and compression loads, never mind cryogenic temperatures.
You are correct that carbon fiber itself is stronger than steel. The problem is to form it into propellant tanks the individual fibers have to be epoxied together. It’s the epoxy, i.e., glue, which makes the structure weaker than the individual fibers. Carbon fiber tanks are more accurately called carbon-fiber composite tanks because they are a composite material containing the carbon fiber and the epoxy. Look up strengths of carbon fiber composite tanks.
Bob Clark
#24 Re: Human missions » Starship is Go... » 2024-03-14 15:04:31
Update from SpaceX. The booster experienced a RUD after the landing relight before contacting the water:
"Super Heavy successfully lit several engines for its first ever landing burn before the vehicle experienced a RUD (that’s SpaceX-speak for “rapid unscheduled disassembly”). The booster’s flight concluded at approximately 462 meters in altitude and just under seven minutes into the mission.“
https://www.spacex.com/launches/mission … p-flight-3
So SpaceX still has not demonstrated the Raptor can relight reliably in flight. In fact, all the Starship landing tests and actual flight tests have shown it is not reliable after relight in flight.
Bob Clark
#25 Interplanetary transportation » Towards manned Japanese spaceflight. » 2024-02-17 08:40:01
- RGClark
- Replies: 4
The Friday launch of the new JAXA rocket the H3 was successful:
JAXA reaches orbit on the second launch of H3.
written by William Graham February 16, 2024
https://www.nasaspaceflight.com/2024/02/jaxa-second-h3/
This H3 version used two core engines and two solid side boosters. But JAXA also plans a version with three core engines and no side boosters.
This all-liquid version will have a payload of 4 tons to SSO, sun-synchronous orbit. Payload to LEO is generally 50% to 60% higher, so the 3 engine no SRB H3 will have approx. 6 tons to LEO capability. This would have the capability of launching a Gemini-class capsule to LEO, which had a 3.8 ton mass.
An all-liquid H3 for a manned launcher would not have the safety issues of using solid rockets. Europe and India are racing to have the next manned orbital launcher. Japan should join the race.
Bob Clark