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Nobody cares; it's good for a laugh. 
SpaceX General Section / Re: SpaceX SmallSat Rideshare Program
« Last post by deltaV on Today at 02:11 am »
Some companies even complained about the mission to the Pentagon because “there was no business reason to fly that mission at that cost,” according to the executive, who spoke on the condition of anonymity to discuss internal deliberations. “We’ve communicated to them, quietly, that you may want competition, but what do your actions say? Because we can’t compete against that.”

Would the Pentagon be significantly bothered if ride shares drive small launchers out of business? The complainers seem to hope so, but I haven't seen any evidence that they would. The Pentagon's priority seems to be ensuring competition for NSSL lane 2, with a bone thrown at other launchers in the form of lane 1.

Let’s see…Smallsat launcher, with access to the Pentagon, directly impacted by SpaceX rideshare missions. Can’t be from China, Russia or India. Europe has no smallsat launchers of note, and the Pentagon would not care about their complaints anyway.

Astra and Virgin Orbit have gone bankrupt and Relativity is not close to flying yet.

There are still many American small launcher companies it could be, including ABSL, Firefly, Northrop Grumman, Rocket Lab, and Stoke Space.
I think this really boils down to the question of demand.  Where does demand for 1000 flights come from?

I see three possibilities

Elons mars plans
Point to point travel
Commercial demand

For each of those you have 2 questions:

Will that scenario will happen at all?
What is the most likely time line?

If Elon continues to push as hard on his Mars plans as he is today then I could see it happening in ten to fifteen years.  However, stuff happens,  he might:

have a heart attack
lose control of SpaceX
get hit by a bus
lose interest as he ages
get randomly murdered by someone demanding to know "Kenneth, what's the frequency?"
...just to list a few

Elon Musk is the single point of failure in this scenario.  He's a variable not a constant.

As for point-to-point travel, I have one word "Concorde".  It didn't fail because the concept couldn't be made to work, it failed for geopolitical reasons, which could easily sink starship too.  Those same considerations make predicting timelines nearly impossible.  It's also possible that market demand just isn't there at the price point they can offer.

The remaining scenario is commercial. In the latter part of this decade I see Starship replacing Falcon and the combination of traditional demand plus starlink resulting in hundreds of flights per year, not 1000+.  I don't see the number of non starlink payloads growing by a massive amount (although I do see the size of those payloads growing). For commercial demand to ever grow to 1000 flights a year I think it would take several decades and the eventual organic growth of a substantial network of space stations/moonbases prompting major growth in the need for launch that isn't present in the current commercial market.  But that is a time horizon so long that predictions about it are nearly worthless and it could happen with a future generation of vehicle that isn't even called starship anymore.

So to summarize...I couldn't figure out what to vote for.   

(Edit: heh I was so caught up and thinking about it that I didn't even realize it was a super old poll and I couldn't vote anyway)

FARRAH, the superstar satellite
by Dwayne A. Day
Monday, April 15, 2024

The Smithsonian’s Steven F. Udvar-Hazy Center, located near Dulles International Airport outside of Washington, DC, has a large viewing gallery overlooking its restoration hangar. Whereas some museum artifacts spend years in the restoration hangar, many others cycle through quickly for a cleaning and minor repair work before returning to storage or display. Recently a surprising one showed up in the hangar, a half-scale model of a formerly top-secret signals intelligence satellite from the Cold War known as FARRAH. FARRAH was named after actress Farrah Fawcett, who rocketed to fame in the late 1970s after appearing on a poster in a swimsuit and then being cast as one of the angels in the popular TV show “Charlie’s Angels.” Unlike Farrah Fawcett, whose poster reportedly sold six million copies, no previous images of a FARRAH satellite have been released, so this was the satellite’s first public, albeit low-key, debut, 42 years after it was launched.

At least two and possibly up to five FARRAH satellites were built, starting in the early 1980s. They were among the last in the family of Program 989 satellites that operated in low Earth orbit and primarily detected signals emitted from Soviet ground-based radars. Program 989 started in the early 1960s under a different designation and satellites continued to operate probably until 2007, with about three dozen launched over 30 years. Most of the satellites were about the size of a large suitcase with multiple deployed antennas from their sides. They were ejected from other satellites soon after those satellites reached their operational orbits. The last few Program 989 satellites—possibly still using the FARRAH designation—were apparently much larger, shaped like tuna cans, and initially scheduled for launch from the Space Shuttle but later shifted to a few Titan II launches before the program ended in the early 1990s.

A villa in LA?

That lot will never be worth that much.  The only fun that owner is ever going to have with that lot is mowing it.
A small villa.  If it's just speculation, and it's no big deal to them, who cares?  Maybe they'll get stuck with it, maybe they'll get a story to tell.
ISS Section / Re: Trash from the ISS may have hit a house in Florida
« Last post by deltaV on Today at 12:40 am »
NASA has confirmed that the item was part of some trash that was released from ISS and was supposed to burn up in reentry and didn't:

Hat tip

An article (doesn't add much though):
If you have questions about what was said, you can listen to the press conference:

Some notes from that conference:

NASA reaching out to industry, JPL, all NASA centers, want proposal to get samples earlier than ~2040 program of record is tracking given funding limits, want within decadal survey MSR cost estimates (roughly $5-7B). Prefer heritage tech. Needs to be the samples collected by Perseverence, but may not bring back all of the samples if that helps reduce costs. Releasing request for funded-study proposals ~tomorrow, responses due May 17, then they'll award some 90 day funded studies, finish by ~fall. No mention of planetary protection. FY '24 planning to spend $310M on MSR, FY '25 requesting $200M for MSR.

My comments:

I'm guessing that details of planetary protection rules will be key to whether the cost cutting miracle that NASA is hoping for happens. I hope NASA is taking a hard look at which planetary protection rules are really necessary and which are nice to have. Even if NASA can't compromise it would help if people knew more about the planetary protection rules, e.g. where is and isn't a special region.

#Starliner is now loaded onto the transporter that will roll it out of our factory tomorrow, April 16. It will head to
@ulalaunch's Vertical Integration Facility to be integrated with the #AtlasV rocket for the Crew Flight Test launch on May 6.
This is why I argue the "optimal" booster engine cluster has the chambers densely packed together in a honeycomb, with nozzles extending downward to form sawtooth hexagons.

The actual curvature of the nozzle is rotationally symmetric (no weird structures or loads), it's just extended to fill the "corners" with more nozzle. This maximizes your achievable Isp vs thrust density curve (with a given chamber), since you don't waste any area on the bottom of the rocket.
Question:  Is it necessary to have sawteeth in the interior of the pattern?

I'd guess gas would flow into in the voids and do the job of the missing sawteeth.

Gas undoubtedly flows, but without the nice optimized bell contour to push against it doesn't contribute to thrust in a significant way.

I expect the net gas flow through those voids is actually outwards (downwards), because of gas being entrained by the exhaust plumes.

What pushes the booster upwards is Newtons 3rd law:
"To every action, there is always opposed an equal reaction; or, the mutual actions of two bodies upon each other are always equal, and directed to contrary parts."

When you accelerate exhaust downwards, there must be a force on the back end of the booster that actually pushes it.
This force exists, and it is gas pressure excerted on the bottom of the rocket.
Mostly on the nozzles, but not only on the nozzles.

At sea level the nozzles are over-expanded. The pressure in the exhaust stream is lower than in the surrounding air, so the exhaust pulls in air from its surroundings. If you have densely packed nozzles, this pulls a partial vacuum between these nozzles, but this partial vacuum reduces the pressure in between nozzles, which increases the expansion, so you end up with an equalibrium where no more air is "pulled in"  (this looks different for the outermost engines that are exposed to the atmosphere, which is why you end up with giant shock diamonds as if you had one giant nozzle the size of the rocket)

As Superheavy climbs, this equalibrium between the entrapped gas between nozzles and the nozzle exhaust remains the same. It's below
sea level atmosphere, but as the booster rises, the "outside" atmosphere pressure gets even lower. Even as the booster leaves the atmosphere, as long as all engines are running there is entrapped gas between the nozzles, replenished by recirculating exhaust and kept at more or less the same pressure it had just after launch. This pressure excerts a force per area on the booster. AKA it generates thrust.

This thrust is exactly the same as you would have if you would increase the nozzle sizes and have them meet in a hexagonal pattern - except in the latter case you could no longer gimbal the inner engines since they would be densely packed.

Of course this "trick" only works if the entrapped gasses can't escape elsewhere. So your outer ring of engines should be "dense" - I think with SpaceX switch to "unshielded" Raptor 3 it no longer will be.
Try Skylab back in the 70's. The ATM had, among other solar instruments, a white light solar coronagraph for imaging

Isn't comparable to a perfectly sized occultation disc 380000 km away which provides much sharper views deeper into the corona.
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