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#26 2021-06-20 07:43:37

Registered: 2019-02-17
Posts: 231

Re: On the lasting importance of SpaceX.

For SpaceNut ... there are two pages of results for topics containing the word SpaceX ... this one was at the top of the list (most recent)

I'll put the document from GW Johnson here ...

Here are the 3 relevant news articles from AIAA's "Daily Launch" email newsletter as regards Spacex's operations at Boca Chica:

6-18-21:  Monteith “Defends” SpaceX Despite Unauthorized SN8 Launch In December
The Hill (6/17) reports that on Wednesday, FAA Associate Administrator Wayne Monteith “defended SpaceX during a congressional hearing,” even “though the company launched a Starship prototype in December without authorization.” Monteith said, “We would not have cleared them to start flight operations again had I not been confident they had modified their procedures effectively and addressed the safety culture issues that we saw.” Earlier this year, Monteith “said SpaceX’s actions were ‘inconsistent with a strong safety culture,’ according to The Verge. These comments came after the company violated the agency’s launch license when it sent a test flight of the Starship prototype rocket SN8 in December.”

6-17-21:  Leaked Documents: SpaceX Violated FAA Warnings In December Launch Of SN8
The Daily Mail (UK) (6/16) reports that SpaceX “ignored at least two warnings from the Federal Aviation Administration (FAA) that the launch of its SN8 rocket last December might not be safe, leaked documents show.” FAA warnings “were based on its launch-weather modelling software, according to the documents, which were seen by the Verge.” Had the rocket “exploded, its shockwave could be strengthened by weather conditions like wind speed and endanger nearby homes, the models suggested.” SpaceX “went ahead with the launch, violating its launch license from the FAA in the process. SN8 ended up launching successfully but crash-landing in a ball of flames.” FAA Associate Administrator for Commercial Space Transportation Wayne Monteith criticized SpaceX “for proceeding with the launch based on ‘impressions’ and ‘assumptions’ rather than procedural checks.”

6-16-21:  Source: SpaceX Unlikely To Launch Starship On First Orbital Flight In July
CNN (6/15) reports that SpaceX is aiming to launch its Starship spacecraft on its first orbital flight in July, but “the company is not likely to hit that goal, CNN Business has learned.” SpaceX’s Starship “launch operations are the subject of an ongoing environmental assessment. Depending on the outcome of that assessment it may also be required to go through a more detailed review culminating in an updated Environmental Impact Statement.” Only “after that process is complete can the Federal Aviation Administration move on to licensing a possible orbital Starship launch. Those reviews and approvals will not be done in time for an early July launch, according to a source familiar with the licensing process.”


The first 2 in the list (the more recent ones) deal with a bureaucratic controversy regarding the SN-8 launch.  Remembering that the FAA bureaucracy is not a monolithic construct,  but aggregated of individuals of varying expertise and opinion,  it is clear Spacex got into trouble with some in the agency over how they managed that launch.  But the Associate Administrator is satisfied they corrected their problems,  or SN-9-on would not have been allowed to fly.  So despite two recent articles in the newsletter being published,  that issue is done.  They already have permissions to fly SN-16 and SN-17 from Boca Chica without boosters.

The third article (16th) is different:  that is a completely different issue.  What is involved here is the launch of a Super Heavy booster,  which has far greater thrust,  far more noise,  and 3400 more metric tons explosive potential (the booster propellant load per the Spacex website) if it blows up at launch.  Considering the enormous risks for lethal noise and incredibly strong explosion blast,  I am totally unsurprised that some sort of significant update of their environmental impact statement is required.  This is not for the FAA,  this is for the EPA,  as I understand the process.  Unlike FAA,  EPA has no mandate to foster and promote the industries that they are intended to regulate.

The offshore launch platform is the longer-term solution for this hazard to human neighbors.  Short term,  if they fly SuperHeavy out of Boca Chica,  the outskirts of Brownsville are only 10 miles away,  and there humans living within 5 miles,  unprotected except by flimsy residential construction,  on both sides of the border.    The FAA cannot grant a license to fly such a mission until this human safety issue is resolved first,  which is integral to that EPA-required environmental impact statement.

As for Musk's tweet about flying SN-16 for a hypersonic test,  let's just say I am initially skeptical.  I presume this would be Starship without Superheavy,  because of the environmental impact troubles.  Starship has been flying with 3 Raptor sea level engines,  for a total of 6 MN thrust.  The takeoff thrust/weight ratio must be at least 1.2,  and much-preferred nearer 1.5,  for decent ascent kinematics.  Musk himself has said so.  The other 3 engines are vacuum Raptors.  You cannot really stick 3 more sea-level Raptors in their place,  because the sea-level bells are too short,  terminating way inside the skirt.  You think engine bay fires were a problem before,  just try doing that!!!

But using the lower figure,  that's 6 MN/1.2 = 5 MN Earth weight at takeoff,  which is roughly 500 metric tons mass.  Assuming 120 ton inert,  and zero payload,  the max propellant load is 380 tons.  If you fly expendably without landing (letting it crash at sea),  the mass ratio is 500/120,  or only about 4.166.  With a sea level exhaust velocity of about 3.2 km/s,  your max theoretical delta-vee is 4.56 km/s.  Knock off around 30% for gravity and drag losses (because of the low T/W factor),  and your max speed would be in the 3.19 km/s ballpark.  At around 300 m/s speed of sound,  that's around Mach 10.

Theoretically,  that's well hypersonic,  which for a "pointy" shape like this starts around Mach 5 (closer to Mach 3 for a blunt shape).  But what good is such a test unless you recover the test article?  Which would be the heat shield tiles on the skin of the vehicle.  After exposure to hypersonic temperatures and wind blast effects.

Try saving back around 25 tons of propellant for the flip and landing.  Now your mass ratio for the ascent burn is 500/(120+25) = 3.44,  for a theoretical delta-vee of 4 km/s.  Knocking off 30% for gravity and drag at poor T/W,  peak ascent speed is nearer 2.8 km/s,  or Mach 9.  I am surprised it could do that much.  So,  it looks like a practical hypersonic test could be done,  despite my earlier skepticism.

The most important thing to demonstrate on a hypersonic test like this would be controlling the vehicle during a hypersonic entry into the belly-flop descent.  That is exactly what it will have to do coming back from orbit.  None of the flight tests so far have come even remotely close to such a demonstration:  all have entered the belly-flop from essentially hovering.  Such will NOT be available during a descent from orbit.  The propellant to stop in midair will NOT be available. 

Now that I know such conditions are indeed reachable,  just flying Starship without a booster,  I changed my mind and think the hypersonic flight test is a good idea.  But only if they can demonstrate hypersonic entry into the belly-flop during such tests.  It may take multiple mid-air losses before they figure it out.  No one has ever done such a thing before. 

If I were in charge of engineering at Spacex,  I would recommend to Musk that hypersonic entry into the belly-flop be demonstrated without the Superheavy,  before attempting an orbital mission with that booster.  By the time that demonstration is done,  the offshore platform could be ready,  and the environmental impact statement update problem associated with the Superheavy goes away.  And more of the orbital mission would have appropriate test experience behind it.


For SpaceNut ... the machine assisting with this process is running a version of Android as part of the Google family of laptops.

It accepted the document from GW Johnson (docx) as input, and allowed me to copy the contents from a Google document screen.

Hopefully it will transfer correctly.

I'll be glad when GW Johnson is back on his own machine.

On the ** other ** hand, it is nice to be able to help out during an extended outage as this one has turned out to be.


Recruiting High Value members for, in association with the Mars Society


#27 2021-06-20 08:17:29

From: New Hampshire
Registered: 2004-07-22
Posts: 23,078

Re: On the lasting importance of SpaceX.

The impacts are even greater for firing up the BFR booster first stage as the propellant load is huge and since thats not flown it needs multiple tries with even a dummy stage placed on top before they try fill a real starship on top of that.
This is no Falcon 1 to Falcon 9 transition due to scale of fuel....
The reentry of starship has been seen how damaging it can be but that also depends on where it breaks up in its downward flight if at all.
Then we have the landing issues for both which are not trivial...


#28 2021-07-14 05:58:45

Registered: 2006-03-23
Posts: 884

Re: On the lasting importance of SpaceX.

China looks like it will copy Musk's Reusable ideas?

Chinese rocket companies are preparing for hop tests … hop-tests/


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