Virgin Galatic Spaceship Two down in the Mojave.

[SKS777FLYER]

NTSB states early activation of unlock mechanism.

First flight with new fuel, and first inflight ignition of new fuel.
Significant different vehicle noise/ride/acceleration/vibration feel to the experienced test pilot of the vehicle, perhaps lending itself to confusion/distraction in accomplishing mission profile checklist procedures?

A post stating this was first inflight use of new fuel was quickly removed a few days ago, so it may still be forbidden info here.

[wiggy]

FWIW as far as the Astronauts were concerned NASA dropped the mandatory test pilot requirement, and made it a "desirable", as early as Group 3 ("The Fourteen") in '63.

NASA Astronaut Group 3 - Wikipedia, the free encyclopedia

It turned out to be a fairly illustrious group.....

[Swedish Steve]

But even if you can get the "spaceship" out of the atmosphere and up to, say, Mach 3 before you switch to rocket engines, you still need to go from Mach 3 to Mach 25,

Can someone explain to a non space man how you measure Mach number when you are out of the atmosphere? Surely in space there is no sound so there cannot be any Mach number? Does this mean Mach 25 in a near vacuum, or Mach 25 at sea level?

I thought that I understood that Mach 1.4 at top of apogee was nearly a standstill because of being in space, and now we have Mach 25 in space?

[what next]

In order to orbit the earth, you need no Mach number - which would be meaningless in vacuum or near vacuum - but a certain speed: The first cosmic speed, 27,800km/hr or 7.7km/s. The often quoted figure of Mach 25 simply comes from dividing that speed by the speed of sound at sea level (0.3km/s) which does not make much physical sense 200km above the surface.

[funfly]

Interesting point about speed outside of the atmosphere. Measuring how fast you are going against…what.
Bit like how fast are you walking when you are on a moving train.

[peekay4]

7.7 km/s is about the velocity required to maintain low-earth orbit.

Due to atmospheric and gravity drag, the velocity required to reach low orbit -- the delta V-- is about 9.4 km/s (33,840 km/h).

As a comparison, SpaceShipTwo will have a delta V of <= 2.0 km/s (7,200 km/h) to fly a suborbital profile.

[what next]

Measuring how fast you are going against…what.

Against nothing. In order to maintain orbit, you have to travel at 7.7km/s. Speed = distance / time. The distance to cover is the circumference of the earth (radius + 200km to stay outside the atmosphere times 2 times pi) and when you come back to the point from which you started - measured against the sun or the stars (the difference will be only a few seconds) in roundabout 90 minutes you have achieved a stable orbit.

[Nemrytter]

Measuring how fast you are going against…what.

Relative to the (gravitational) center of the Earth.

[TyroPicard]

Quote:
Relative to the (gravitational) center of the Earth.

Hmmm... In a circular orbit you are neither moving towards nor away from the centre of the Earth ... Speed zero?

[wiggy]

SS

I thought that I understood that Mach 1.4 at top of apogee was nearly a standstill because of being in space, and now we have Mach 25 in space?

Don't overthink it, folks are just using "Mach number" as a handy and convenient yardstick to compare what SS2 might be capable of in the way of velocity vs. what is required for genuine orbital flight. As has been mentioned for a stable circular low earth orbit at any sort of sensible altitude (say a minimum of 160 km or a bit more) you need a "horizontal " velocity of around 8000 metres/ second. Given Mach 1 in air is usually quoted at around 300-330 metres per second orbital velocity equates to a Mach number of around Mach 25...whether it's useful or confusing to use Mach number is another matter.

Hmmm... In a circular orbit you are neither moving towards nor away from the centre of the Earth ... Speed zero?

Sometimes it pays to go off at a tangent.............

[pattern_is_full]

It should be noted that the speed of sound is distinctly non-zero (275 m/s), all the way up past 100 km (target altitude of original SS1).

http://upload.wikimedia.org/wikipedi...e_1962.svg.png

There is still (very thin) atmosphere up there (and thus molecules to transmit sound energy).

The Kármán Line - BTW - is the altitude where the speed needed for aerodynamic lift/flight become faster than orbital velocity (so you might just as well orbit as "fly").

[Higs99]

And hence the Kármán Line is the accepted definition of the start of (Outer) Space ....

[hamster3null]

Originally Posted by pattern_is_full

The Kármán Line - BTW - is the altitude where the speed needed for aerodynamic lift/flight become faster than orbital velocity (so you might just as well orbit as "fly").

At 100 km you already can't fly, but you still can't orbit (because there's so much air drag that your orbit will decay in a matter of hours). At 300 km you can last about a month in orbit. ISS is at 400 km and it still needs periodic boosts (though its orbital decay is tolerably low).

[pumpkin53]

angular velocity

ah, yes, the dynamics course in early college. What is needed is a certain minimum "angular velocity". Velocity is a vector number, meaning a magnitude and a direction. In orbit, the direction is constantly changing, since gravity pull is acting towards earth center of mass, and inertia, wanting to keep the craft going straight.
So, yes, zero speed relative the distance from the center of the earth, but still a very significant angular velocity!

[ChristiaanJ]

hotelpresident,
Unfortunately your "source" is a highly doubtful website, and there is no such thing as a British Aerospace Agency.
Don't believe all the "urban fiction" on the net......

[tdracer]

Interesting read about Seibold:

Injured test pilot's passion for flying shines through | HeraldNet.com - Aerospace blog

[janrein]

Aerodynamic forces and feather booms

@patternfull
That link to atmosphere up to Karman line comes in handy.

Inputs from various sources combined with atmosphere structure as per link:
M1 at 45 kft ==> 295 m/s at 0.25 kg/m3 density
M1.4 at 70 kft ==> 413 m/s at 0.10 kg/m3 density
(all approximate)

Would yield for dynamic pressure:
q = 11 kPa at 45kft and M1
q = 8.5 kPa at 70kft and M 1.4

@RichardC10:
Confirms your comment a few pages back:
q does not decrease that much indeed over that part of the flight profile.

That would make it less likely to expect catastrophic failure upon unlocking at M1, while unlocking at M 1.4 would be normally acceptable,
IF(!) q were the only factor in play.

However another possible factor may be:
M1 is in the transsonic regime, while M 1.4 is well beyond that.

Meaning: with lift vectors in the transsonic regime jumping backwards on the tailboom elevators, and likely different in place and time between top and bottom surfaces, aerodynamic effects can be more problematic in the transsonic regime.

Which seems more plausable a factor than a design flaw or malfunction of the pneumatic actuation system as a cause of the uncommanded feather.

jr

[Rodney Rotorslap]

Anyone else struggling with the irony that this vehicle has a feathering system to present maximum drag while a feathering system in a propeller is designed to present minimum drag?

[janrein]

"Feathering"

@Rodney

Anyone else ...

Indeed! And what appears initially as irony may in some cases even cause confusion. Human factors, language, ... all that.

(not in this case I believe)

jr

[SKS777FLYER]

Look at flame pattern of amazing inflight video on SS2 on earlier flight with previous version of fuel. Obviously, the previous fuel proved unsat after ground and flight tests. As the accident flight was the first for the new fuel, there are no videos or experience with its flight characteristics. It may have a vibration characteristic, initial acceleration, sound transmitted thru the vehicle and or slightly different thrust vector than previous rocket rides in the vehicle that the veteran test pilots experienced/ expected.