Dumb SS1 questions

In article OJQBc.157831$Ly.127326@attbi_s01,
Scott Moore wrote:
1. assuming the next "big prize" would be an orbital vehicle, what is the
lowest altitude an object can be orbited at, if only for a circuit or so ?

At about 150km it's marginally possible. 200km is more comfortable.

Reaching orbit is mostly a problem of horizontal velocity, not altitude.
The big problem is not getting up to orbital altitude, but accelerating to
about 8km/s once you're there.

2. If SS1 wanted to go somewhere instead of straight up, would it be able to,
say, cross the United States at several mach, above the atmosphere ?

No. The artillery rule of thumb is that maximum horizontal range is twice
the altitude reached when fired straight up, which would give SS1 maximum
range of only a couple of hundred kilometers. The wings would improve the
situation somewhat, but still, this is not a transcontinental vehicle.

3. How much bigger (more thrust) would SS1 have to have to achieve orbit ?

It would have to be completely redesigned. Modest upgrades to its engine
hardware could probably get it to orbital altitude, but there's no way it
can possibly carry enough fuel to accelerate to orbital velocity.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

Scott Moore wrote in message news:OJQBc.157831$Ly.127326@attbi_s01...
If you can forgive a dumb space question or two:

1. assuming the next "big prize" would be an orbital vehicle, what is the lowest
altitude an object can be orbited at, if only for a circuit or so ?

At 90-100 miles, drag should be low enough to complete one orbit.

2. If SS1 wanted to go somewhere instead of straight up, would it be able to,
say, cross the United States at several mach, above the atmosphere ?

If you go straight up...well, you go straight up, with no sideways
velocity to cover any distance over the ground. You need some
horizontal speed, too.

3. How much bigger (more thrust) would SS1 have to have to achieve orbit ?

SS1 had plenty of thrust - after all, it went up at first, not down.

The issue is more a matter of "how much fuel is needed to get to
orbit?"

Orbital velocity is a matter of moving far enough sideways to avoid
the horizon when gravity pulls you down. What SS1 did is not approach
orbit. Rather, it approached space - it got above the atmosphere.
That's a nice step toward orbit (because atmospheric drag will slow
you down and thus hit the horizon), but it's just a small step.

The big step is moving fast enough to miss the horizon.

That involves moving tangent to the ground at about 17500mph for a low
orbit. Another 2000-3000mph is wasted going up and getting above the
atmosphere.

To get to orbit, a rocket with highly efficient engines (unlike SS1)
would need about 90% of its mass to be fuel and oxidizer. SS1 would
need about 95-97% of its mass to be fuel and oxidizer. This would
probably demand more thrust (at first), but the more important issue
is the amount of fuel.


Mike Miller

"Scott Moore" wrote in message news:OJQBc.157831

3. How much bigger (more thrust) would SS1 have to have to achieve orbit ?

More (longer/bigger) = more fuel = larger structure = more weight = more
fuel = etc.

;-)

You can look at it several ways, but one interesting comparison is this:

SS1 max speed = about 2500 fps (IIRC)
Orbital speed = about 25000 fps

You need ten times more speed, but that's not the whole story either. You
have to impart a bunch of energy to a mass to get it into orbit. You can
sort of approximate this with the sum of the kinetic and potential energy
per pound of mass for a low orbit. I can't recall what the potential energy
is for orbits (I would have thought it's simply mgh, but something tells me
that's _almost_ right) but kinetic energy is much greater at 0.5mv^2. The
kinetic energy scales with the square of velocity. IOW, you need to impart
100 times more energy to the vehicle _per_pound_ to get it into orbit
(actually more, because you have to make up losses due to drag). Remember,
too, that they have to carry fuel onboard to perform a deorbit manuever
later on.

Maybe the answer is to fit a rocket engine or two to WhiteKnight. If White
Knight could carry SS1 to 60 miles and Mach 22 then maybe there's a chance
...

;-)

Henry Spencer wrote:

In article OJQBc.157831$Ly.127326@attbi_s01,
Scott Moore wrote:
1. assuming the next "big prize" would be an orbital vehicle, what is the
lowest altitude an object can be orbited at, if only for a circuit or so ?

At about 150km it's marginally possible. 200km is more comfortable.

Of course, Rutan has already done a single orbit vehicle, at a far lower
altitude...

--
Scott Lowther, Engineer
Remove the obvious (capitalized) anti-spam
gibberish from the reply-to e-mail address

Scott Moore wrote in message news:OJQBc.157831$Ly.127326@attbi_s01...
If you can forgive a dumb space question or two:

1. assuming the next "big prize" would be an orbital vehicle,
what is the lowest altitude an object can be orbited at,
if only for a circuit or so ?

Vostok's orbit is around 200 Km.

And according to this calculation page below:

http://liftoff.msfc.nasa.gov/academy.../vel_calc.html

http://liftoff.msfc.nasa.gov/Scripts...84%2C999999999

http://liftoff.msfc.nasa.gov/Scripts....pl?Radius=185

Anything below 185 Km is not stable and to orbit at 185 km it took the
orbital velocity of 28.044 kilometers / hour.

2. If SS1 wanted to go somewhere instead of straight up,
would it be able to, say, cross the United States at several mach,
above the atmosphere ?

Possible, if it was heavily redesigned. But then again, when that
happened, it's much better to called it Space Ship Two, or just plain
Super Sonic Transport.

3. How much bigger (more thrust) would SS1 have to have to achieve orbit ?

It's not only thrust is needed, but also Total Impulse.

I think that the whole Total Impulse of the R-7 that tool Vostok to
orbit is 752,15392 millions Newton-seconds , while Space Ship One's
Total Impulse is around 0,78% of that.

If things stay the way they're, White Knight would do no good, it's
better to stick Space Ship One on top of the R-7. Though there's still
the problem of slowing down from orbital velocity, can Space Ship One
reduce it speed safely from the orbital velocity of around 28.000 Km
/hour at the orbit of around 200 km?

Thanks.

Scott Lowther writes:

Henry Spencer wrote:

In article OJQBc.157831$Ly.127326@attbi_s01,
Scott Moore wrote:
1. assuming the next "big prize" would be an orbital vehicle, what is the
lowest altitude an object can be orbited at, if only for a circuit or so ?

At about 150km it's marginally possible. 200km is more comfortable.

Of course, Rutan has already done a single orbit vehicle, at a far lower
altitude...

Not using *anybody's* reasonable definition of "orbit."
--
Joseph J. Pfeiffer, Jr., Ph.D. Phone -- (505) 646-1605
Department of Computer Science FAX -- (505) 646-1002
New Mexico State University http://www.cs.nmsu.edu/~pfeiffer
Southwestern NM Regional Science and Engr Fair: http://www.nmsu.edu/~scifair

Joe Pfeiffer wrote:

Scott Lowther writes:

Henry Spencer wrote:

In article OJQBc.157831$Ly.127326@attbi_s01,
Scott Moore wrote:
1. assuming the next "big prize" would be an orbital vehicle, what is the
lowest altitude an object can be orbited at, if only for a circuit or so ?

At about 150km it's marginally possible. 200km is more comfortable.

Of course, Rutan has already done a single orbit vehicle, at a far lower
altitude...

Not using *anybody's* reasonable definition of "orbit."

Pfah. Once all the way around the planet without touching down. Close
enough for government work...

--
Scott Lowther, Engineer
Remove the obvious (capitalized) anti-spam
gibberish from the reply-to e-mail address

Joe Pfeiffer wrote in message ...
Scott Lowther writes:

[...]
Of course, Rutan has already done a single orbit vehicle, at a far lower
altitude...

Not using *anybody's* reasonable definition of "orbit."

From Webster's online dictionary:

Main Entry: 2orbit
Function: noun
[...]
b : a circular path
Main Entry: 3orbit
Function: verb
[...]
intransitive senses : to travel in circles

"Jon Berndt" wrote in message ...
"Scott Moore" wrote in message news:OJQBc.157831

3. How much bigger (more thrust) would SS1 have to have to achieve orbit ?

More (longer/bigger) = more fuel = larger structure = more weight = more
fuel = etc.

;-)

You can look at it several ways, but one interesting comparison is this:

SS1 max speed = about 2500 fps (IIRC)
Orbital speed = about 25000 fps

You need ten times more speed, but that's not the whole story either. You
have to impart a bunch of energy to a mass to get it into orbit. You can
sort of approximate this with the sum of the kinetic and potential energy
per pound of mass for a low orbit. I can't recall what the potential energy
is for orbits (I would have thought it's simply mgh, but something tells me
that's _almost_ right) but kinetic energy is much greater at 0.5mv^2. The
kinetic energy scales with the square of velocity. IOW, you need to impart
100 times more energy to the vehicle _per_pound_ to get it into orbit
(actually more, because you have to make up losses due to drag). Remember,
too, that they have to carry fuel onboard to perform a deorbit manuever
later on.

Maybe the answer is to fit a rocket engine or two to WhiteKnight. If White
Knight could carry SS1 to 60 miles and Mach 22 then maybe there's a chance
..

;-)

Yeah, I think it is more like 8 or 9 times faster needed for orbit
than SS1 achieved, but it hardly matters.

In reality, probably 100 times more power is needed for something of
SS1's mass to get into orbit - obviously, putting in 100 times more
fuel won't do that, as that would increase the weight dramatically.

As it is, using SS1's engines (A nitrous-oxide HBTP hybrid booster)
can't achieve anything like a high enough ISP (power/weight ratio,
effectively) to get anywhere close to orbit - a complete re-design
would be needed.

From what I've read of Rutan's comments, he intends to do it in stages
- first making a 6 person craft to go to 150 Km and maybe double the
peak velocity, and so on. Whether he will be able to achieve orbit
without massive funding remains to be seen.

The challenges of getting to orbit compared with leaving the
atmosphere is much like comparing the challenge of getting off the
ground in the first place to leaving the atmosphere. Ie, it's huge.

Mike Miller wrote:
Scott Moore wrote in message news:OJQBc.157831$Ly.127326@attbi_s01...
If you can forgive a dumb space question or two:

1. assuming the next "big prize" would be an orbital vehicle, what is the lowest
altitude an object can be orbited at, if only for a circuit or so ?

At 90-100 miles, drag should be low enough to complete one orbit.

It depends somewhat on the density of the object.

If it's really low (a balloon) then it'll need to orbit much higher than
if it's a solid 100m long bar of tungsten.

At 100Km, and at orbital speeds, the pressure exerted by the atmosphere
on the vehicle is around 2Kg force/square meter.
This will cause a balloon to slow at around 20000m/s (it'll effectively come
to a stop in half a second and drift down) but the bar of tungsten by only
a billionth of a the same amount, and it'd take some 15 years to slow
as much.
(though as it slows down, it drops, so it'll come in faster, maybe a
few months.)