Definition of Spaceflight
James A Davis
Spaceflight is usually described in terms of height above sea level, 50
miles and 100 km being common standards. I would like to offer a
different definition.
Spaceflight is unique in at least 3 respects:
1.) It involves being surrounded by vacuum.
2.) It involves the sensation of weightlessness.
3.) It involves very high speeds.
Proposed definition:
A spaceflight is occuring when the following three conditions are met
simultaneously:
1.) The static pressure outside of a vehicle is less than the average
atmospheric static pressure at 100 km above sea level.
2.) Any sensation of weight is due only to inertial forces.
3.) The sum of the specific potential energy (relative to the earth's
surface) and specific kinetic energy (relative to the earth's center)
of a vehicle is greater than the specific kinetic energy of an object
moving at sea level circular speed (relative to the earth's center).
Circular speed at sea level is defined as Vc = SQRT(gR).
It is the third condition which separates the pretenders from the
contenders. All current spaceflights would meet the above definition
except for the 2 Mercury-Redstone flights and the much later Soyuz
"Anomaly." I don't think this definition in any way denigrates the
importance of the Mercury-Redstone flights in the history of US manned
space flight or Shepard and Grissom's role in it. I *do* think that
including the Redstone flights while excluding the X-15 astronaut
flights does tend to denigrate the achievements of the X-15 pilots.
I think this definition is more consistent with historical perception.
Does anyone know when the first rocket climbed to 50 miles or 100 km? If
this was the first unmanned spaceflight why was Sputnik considered so
significant?
Jim Davis
Dave Michelson
In article <35526F...@primary.net>,
James A Davis <jimd...@primary.net> wrote:
>
>I think this definition is more consistent with historical perception.
>Does anyone know when the first rocket climbed to 50 miles or 100 km? If
>this was the first unmanned spaceflight why was Sputnik considered so
>significant?
According to newsreels of the time, Sputnik *implied* that the Soviets
had an operational ICBM. The U.S. did not. This demonstration of
military capability captured the attention of both the U.S. public and
the rest of the world, for obvious reasons.
Footnote: neither of the first U.S. satellite launchers (Vanguard and
Redst^H^H^H Jupiter C) were ICBM's. The first successful satellite
launch using a U.S. ICBM (Atlas) didn't take place until over a year
after Sputnik (SCORE, launched in December 1958.)
--
Dave Michelson
da...@ee.ubc.ca
James A Davis
Dave Michelson wrote:
> According to newsreels of the time, Sputnik *implied* that the Soviets
> had an operational ICBM. The U.S. did not. This demonstration of
> military capability captured the attention of both the U.S. public and
> the rest of the world, for obvious reasons.
>
> Footnote: neither of the first U.S. satellite launchers (Vanguard and
> Redst^H^H^H Jupiter C) were ICBM's. The first successful satellite
> launch using a U.S. ICBM (Atlas) didn't take place until over a year
> after Sputnik (SCORE, launched in December 1958.)
Dave, this is exactly my point. A rocket capable of achieving an
altitude of 100 km is of rather limited utility. One capable of orbital
speeds is a quantum leap in military and commercial potential. Hence the
importance of Sputnik.
Similarily, sending a man to an altitude of 100 km is of questionable
value. Putting him in orbit opens up exciting possibilities. That is why
my definition of spacefight emphasizes this ability.
Jim Davis
Robert S. Gregg
James A Davis wrote in message <35526F...@primary.net>...
>A spaceflight is occuring when the following three conditions are met
>simultaneously:
This is an interesting exercise! I'm a little skeptical of the second
criterion, though:
>2.) Any sensation of weight is due only to inertial forces.
The phrase "sensation of weight" would seem to imply a manned crew, since
inanimate objects don't have sensations. Since most unmanned satellites
probably do experience spaceflight, by anyone's definition, this one probably
needs to be restated in terms of gravity. Not sure quite how to say it,
though.
Hmm... come to think of it, haven't there been papers theorizing that both
gravity and inertia are similar byproducts of zero point vacuum fluctuations?
>3.) The sum of the specific potential energy (relative to the earth's
>surface) and specific kinetic energy (relative to the earth's center)
>of a vehicle is greater than the specific kinetic energy of an object
>moving at sea level circular speed (relative to the earth's center).
>Circular speed at sea level is defined as Vc = SQRT(gR).
Now, I just *know* I'm gonna look like a fool here (it's been a hell of a long
time since freshman physics!), but would objects in the Lagrange points still
meet this definition?
Bob Gregg
rgr...@scott.net
Dave Michelson
In article <355282...@primary.net>,
Well, the Mercury-Redstone flights demonstrated that the U.S. had a
*capsule* capable of manned orbital flight. Compared to an orbital
mission, they flew a somewhat similar ascent profile, briefly entered
a similar aerodynamic environment, and flew a somewhat similar descent
profile. They certainly had more in common with the Mercury-Atlas
flights than they did with, say, SR-71 flights. For that matter, the
X-15 high altitude flights all flew ballistic trajectories, briefly
entered an aerodynamic environment which precluded the use of
aerodynamic control surfaces, had to deal with re-entry, etc.
So, *I* don't have a great problem referring to the sub-orbital
flights as space flights.
However, your point is an interesting one. We take arbitrary
definitions for granted at our peril!
--
Dave Michelson
da...@ee.ubc.ca
Craig Bingman
In article <flugenn0ck-08...@z3.zilch.net>,
Mike Flugennock <fluge...@sinkers.org> wrote:
>In article <35526F...@primary.net>, jimd...@primary.net wrote:
>Also, while they didn't reach orbit, didn't Shepard and Grissom's
>Mercury/Redstone flights qualify (admittedly barely) as "spaceflight" in
>that they were surrounded by vacuum and experienced zero-g? Didn't they
>also stay in vacuum longer than the X-15 flights?
We get into this problem of defining what constitutes a vacuum. There
are as many definitions of that as there are fields that involve work
at low pressures.
Craig
Henry Spencer
In article <35526F...@primary.net>,
The first successful V-2 prototypes, 1942.
--
Being the last man on the Moon | Henry Spencer
is a very dubious honor. -- Gene Cernan | he...@zoo.toronto.edu
James A Davis
Robert S. Gregg wrote:
> >2.) Any sensation of weight is due only to inertial forces.
>
> The phrase "sensation of weight" would seem to imply a manned crew, since
> inanimate objects don't have sensations. Since most unmanned satellites
> probably do experience spaceflight, by anyone's definition, this one probably
> needs to be restated in terms of gravity. Not sure quite how to say it,
> though.
This does need to be tightened up. How about "Any weight is due only to
accelerations other than those produced by gravitational forces"?
> Hmm... come to think of it, haven't there been papers theorizing that both
> gravity and inertia are similar byproducts of zero point vacuum fluctuations?
I am aware that the General Theory of Relativity states that inertia and
gravity are the same. I know nothing of zero point vacuum fluctuations.
Newtonian mechanics is adequate for the task at hand though.
> >3.) The sum of the specific potential energy (relative to the earth's
> >surface) and specific kinetic energy (relative to the earth's center)
> >of a vehicle is greater than the specific kinetic energy of an object
> >moving at sea level circular speed (relative to the earth's center).
> >Circular speed at sea level is defined as Vc = SQRT(gR).
>
> Now, I just *know* I'm gonna look like a fool here (it's been a hell of a long
> time since freshman physics!), but would objects in the Lagrange points still
> meet this definition?
Oh, definitely. What would make you think otherwise?
Jim Davis
James A Davis
Henry Spencer wrote:
> >Does anyone know when the first rocket climbed to 50 miles or 100 km?
>
> The first successful V-2 prototypes, 1942.
This is, of course, correct. It's amazing how rhetorical questions lose
their impact after someone answers them!
Jim Davis
James A Davis
Dave Michelson wrote:
> Well, the Mercury-Redstone flights demonstrated that the U.S. had a
> *capsule* capable of manned orbital flight. Compared to an orbital
> mission, they flew a somewhat similar ascent profile, briefly entered
> a similar aerodynamic environment, and flew a somewhat similar descent
> profile. They certainly had more in common with the Mercury-Atlas
> flights than they did with, say, SR-71 flights. For that matter, the
> X-15 high altitude flights all flew ballistic trajectories, briefly
> entered an aerodynamic environment which precluded the use of
> aerodynamic control surfaces, had to deal with re-entry, etc.
I have a problem with defining the Redstone flights as space flights
because they resembled the subsequent Atlas flights and the X-15 flights
as non-space flights because they didn't. Every flight should be
evaluated on its own merits. If the US abandoned the Mercury capsule
after the Redstone flights and went to the X-20 Dynasoar would the X-15
flights be space flights and the Redstone flights footnotes?
> So, *I* don't have a great problem referring to the sub-orbital
> flights as space flights.
I just think it's inconsistent. It's like saying Michael Jordan and a
bird can both fly because they can both leave the ground, travel through
the air, and return safely to the ground.
> However, your point is an interesting one. We take arbitrary
> definitions for granted at our peril!
Jim Davis
Bev Clark/Steve Gallacci
I dunno. I'd rather keep it simpler, defining "spaceflight" as extended
exoatmospheric ops rather than speed or zerogee criteria.
I could see where speed and zero gee would not apply to an obvious space
op, an energy intesive, direct to Clarke orbit shuttle, for example.
And zero gee is very much a poor criterium, any ballistic tragectory,
regardless of speed or altitude, will give you that.
Yeah, getting to orbital altitude and staying there for any real length of
time seems to make more sense.
Robert S. Gregg
James A Davis wrote in message <35534A...@primary.net>...
>This does need to be tightened up. How about "Any weight is due only to
>accelerations other than those produced by gravitational forces"?
Still not specific enough. Any weight of what? Weight can only really be
defined as a relative motion between two bodies, not for a single body, so a
lone satellite still has problems with this condition. On the other hand,
wouldn't any satellite still have *some* weight relative to earth, no matter
how high its orbit? Not to mention its weight relative to Sol...
>I am aware that the General Theory of Relativity
>states that inertia and gravity are the same.
I didn't even remember that. Hmm, time to head to Barnes and Noble for a
Feynman book...
>> Now, I just *know* I'm gonna look like a fool here (it's been a hell of a
long
>> time since freshman physics!), but would objects in the Lagrange points
still
>> meet this definition?
>
>Oh, definitely. What would make you think otherwise?
Because I couldn't remember the formulas. Depending on how big the potential
energy term is, it looked on first blush like something had to be circling the
earth faster than earth's rotational speed to qualify. Actually, I was kind
of hoping you'd post the formulas!
Now here's an odd thought. Is the *earth* experiencing spaceflight, by this
definition?
Bob Gregg
rgr...@scott.net
Christopher Michael Jones
I agree, I don't think that there needs to be any sophisticated definitions.
Space flight is anything exoatmospheric (preferably controlled flight) and
an orbit seems to be well defined by itself. There might be some gray
area around sub-orbital flights that loop a significant portion around
the Earth (or whatever planet), but I think its still fairly obvious this
is not an orbit. Other than that, the only possible gray area I can
think of is "deep space" sub-orbital flights that have enough energy
to be a stable orbit above the atmosphere if it were directed in a
different direction at the appropriate altitude.
Otherwise, velocity and inertial criteria merely muddy the watters.
Bev Clark/Steve Gallacci (bev...@netcom.com) wrote:
: I dunno. I'd rather keep it simpler, defining "spaceflight" as extended
James A Davis
Bob Gregg wrote:
> >This does need to be tightened up. How about "Any weight is due only to
> >accelerations other than those produced by gravitational forces"?
>
> Still not specific enough. Any weight of what? Weight can only really be
> defined as a relative motion between two bodies, not for a single body, so a
> lone satellite still has problems with this condition. On the other hand,
> wouldn't any satellite still have *some* weight relative to earth, no matter
> how high its orbit? Not to mention its weight relative to Sol...
I define weight as the normal force one object exerts on another in
reaction to inertial or gravitational forces. An example of the former
is the normal force a spacecraft exerts on an occupant if it is
accelerating (either in translation or rotation). An example of the
latter is the normal force the earth exerts on us because gravity is
pulling us toward the center of the earth. My definition of spaceflight
would allow the former but exclude the latter. I agree however that I'm
not expressing it well.
> >> Now, I just *know* I'm gonna look like a fool here (it's been a hell of a
> long
> >> time since freshman physics!), but would objects in the Lagrange points
> still
> >> meet this definition?
> >
> >Oh, definitely. What would make you think otherwise?
>
> Because I couldn't remember the formulas. Depending on how big the potential
> energy term is, it looked on first blush like something had to be circling the
> earth faster than earth's rotational speed to qualify. Actually, I was kind
> of hoping you'd post the formulas!
The Lagrange points are defined as the points where a small body can
remain at rest with respect to two larger bodies. There are 5 of them. A
body at any of them easily has enough potential energy to qualify by my
definition. There all pretty far from earth.
The formula you want is can be found in Kaplan, "Modern Spacecraft
Dynamics and Control" and a lot of other works. It's one of the few
closed form solutions to the restricted three body problem.
> Now here's an odd thought. Is the *earth* experiencing spaceflight, by this
> definition?
The earth, no. All other celestial bodies, yes. A problem arises when we
consider people born on the moon, Mars, space colonies, etc. but that's
a ways off.
Jim Davis