NASA X-43: For When You Want to Hit Mach 9.6

This was my favorite model when I was kid....

..."The North American X-15 was a hypersonic rocket-powered aircraft operated by the United States Air Force and the National Aeronautics and Space Administration as part of the X-plane series of experimental aircraft. The X-15 set speed and altitude records in the 1960s, reaching the edge of outer space and returning with valuable data used in aircraft and spacecraft design. The X-15's official world record for the highest speed ever recorded by a manned, powered aircraft, set in October 1967 when William J. Knight flew Mach 6.72 at 102,100 feet (31,120 m), a speed of 4,520 miles per hour (7,274 km/h; 2,021 m/s), has remained unchallenged as of November 2017.^[1][2]

During the X-15 program, 13 flights by eight pilots met the Air Force spaceflight criterion by exceeding the altitude of 50 miles (80 km), thus qualifying these pilots as being astronauts. "....

What is the speed of sound at that altitude? I thought mach numbers were relative to local speed of sound and at that altitude there was not enough air for sound. Also what is local (at that altitude) temperature(which also changes speed of sound)?

I think your are correct in asserting that speed of sound rolls off with pressure decreasing, and with temperature decreasing.

Note that when we were discussing nozzle speeds of certain rocket engines, we mentioned about Mach 8.5 - that is for ground testing at sea level (101 kPa) and a normal temperature 25 °C day. Mach 1 is 1225 kph at those conditions and nozzle exhaust velocity could easily be 10412 kph! Note, this speed does not change much as the rocket flies out of the atmosphere, only slightly as there is less back-pressure.

at 50,000 ft altitude ( 15,240 m) pressure is 11.6 kPa and -56.6 °C, the speed of sound is 1062. This means our rocket nozzle speed is about Mach 9.8 up there.

Does this help you with the facts? Also you will recall that ground control usually issues a command for max burn (they have another word for it), where nozzle pressures are increased considerably once atmospherics are reduced, and more acceleration will be gained (without the drag ruining things). This is how we get to speeds such as escape velocity. Escape is 11186 m/s, 40270 kph, sea level Mach 32.8, 25022 mph. That is way fast.

THINK ABOUT IT -- An air-breathing, hyper-velocity vehicle "side-steps" restrictions of the ICBM Treaties.

Treaties...

Because everyone is in full agreement.

I know of two fat, childish, insane playground bullies who don't care at all about treaties.

I always liked the F 104 Starfighter.

It was a hand full to fly and especially to land at 190 knot approach speed.

Codename: Lawndart

Codename: Widowmaker

Also uses a much shallower trajectory eliminating re entry concerns and making intercept harder.

Maybe getting closer to the Holy Grail, Single Stage to Orbit (SSTO)! The way we're doing it now is like buying a new car and driving it once.

https://en.wikipedia.org/wiki/Single-stage-to-orbit

That old car keeps racking up pointless miles in orbit... There should (now)be a fine for littler to fund the cleanup effort.

It used to be called Salvage Rights on the High Seas.

Except my boat is traveling ~17.5KMPHS

Talk about potential for crash debris to create more potential for crashing.. and more debris.. and more..

oh boy..

Two words: Orbital flypaper.

I love flypaper!.. Except when I accidentally bump into it.

...orbital flypaper...

Got you thinking didn't I? See the thread about the new astronaut recovery from EVA system. They hit a panic button, and it navigates them back to the hatch.

I took it one further in my reply, and added orbital flypaper applied to the outside of the spacecraft, so they can hang on better once returned. The issue still remains how to peel them off, ever so careful not to damage the spacesuit to catastrophic vent, and get them back inside. Details, shmetails, come on NASA buy it up.