Multiple Engines???

(Henry Spencer) :

In article ,
Earl Colby Pottinger wrote:
Unless you're planning on using rocket thrust to turn it around (as
Kistler was going to do), what you care about is not where separation
occurs, but where the booster reenters, because it's going to coast a
long way farther downrange...

I don't understand why it must be so far downrange? What is wrong with
going
just straight up, separate, then straight down or as near to that as
possible?

You want the first stage to contribute a fair bit of horizontal velocity,
not just altitude, to the second stage. The dominant problem of getting
into orbit is velocity. A first stage that just goes straight up requires
the second stage to have near-SSTO performance, and the big reason for
using two stages in the first place is the belief that SSTO is Too Hard.

Also, a vertical reentry from high altitude is a lot harsher than one with
a horizontal component, because it takes you down into thick air before
you've had a chance to decelerate much. From 100km, it's manageable; from
much higher than that, it gets pretty nasty unless you've got something
like a deployable drag brake.

I knew all that, but for some reason it just did not click in. Thanks

Earl Colby Pottinger

--
I make public email sent to me! Hydrogen Peroxide Rockets, OpenBeos,
SerialTransfer 3.0, RAMDISK, BoatBuilding, DIY TabletPC. What happened to
the time? http://webhome.idirect.com/~earlcp

(Henry Spencer) :

In article ,
Earl Colby Pottinger wrote:
Unless you're planning on using rocket thrust to turn it around (as
Kistler was going to do), what you care about is not where separation
occurs, but where the booster reenters, because it's going to coast a
long way farther downrange...

I don't understand why it must be so far downrange? What is wrong with
going
just straight up, separate, then straight down or as near to that as
possible?

You want the first stage to contribute a fair bit of horizontal velocity,
not just altitude, to the second stage. The dominant problem of getting
into orbit is velocity. A first stage that just goes straight up requires
the second stage to have near-SSTO performance, and the big reason for
using two stages in the first place is the belief that SSTO is Too Hard.

Also, a vertical reentry from high altitude is a lot harsher than one with
a horizontal component, because it takes you down into thick air before
you've had a chance to decelerate much. From 100km, it's manageable; from
much higher than that, it gets pretty nasty unless you've got something
like a deployable drag brake.

I knew all that, but for some reason it just did not click in. Thanks

Earl Colby Pottinger

--
I make public email sent to me! Hydrogen Peroxide Rockets, OpenBeos,
SerialTransfer 3.0, RAMDISK, BoatBuilding, DIY TabletPC. What happened to
the time? http://webhome.idirect.com/~earlcp

In article ,
Niels J=?ISO-8859-1?B?+A==?=rgen Kruse wrote:
...A first stage that just goes straight up requires
the second stage to have near-SSTO performance, and the big reason for
using two stages in the first place is the belief that SSTO is Too Hard.

Altitude would allow longer burn time - smaller engines.

Oh, there's no denying that it helps somewhat; the question is whether it
helps enough to be worth the added problems with staging and first-stage
recovery.

Also, a vertical reentry from high altitude is a lot harsher than one with
a horizontal component...

Assuming a horizontal velocity component, would it be terrible to take the
1. stage back with something like a CargoLifter?

Not a big problem, if there's a suitable landing spot for the first stage,
and if it's physically compatible (mass, size, etc.) with a suitable cargo
vehicle.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

In article ,
Niels J=?ISO-8859-1?B?+A==?=rgen Kruse wrote:
...A first stage that just goes straight up requires
the second stage to have near-SSTO performance, and the big reason for
using two stages in the first place is the belief that SSTO is Too Hard.

Altitude would allow longer burn time - smaller engines.

Oh, there's no denying that it helps somewhat; the question is whether it
helps enough to be worth the added problems with staging and first-stage
recovery.

Also, a vertical reentry from high altitude is a lot harsher than one with
a horizontal component...

Assuming a horizontal velocity component, would it be terrible to take the
1. stage back with something like a CargoLifter?

Not a big problem, if there's a suitable landing spot for the first stage,
and if it's physically compatible (mass, size, etc.) with a suitable cargo
vehicle.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

(Henry Spencer) wrote in message ...
In article ,
Niels J=?ISO-8859-1?B?+A==?=rgen Kruse wrote:
Assuming a horizontal velocity component, would it be terrible to take the
1. stage back with something like a CargoLifter?

Not a big problem, if there's a suitable landing spot for the first stage,
and if it's physically compatible (mass, size, etc.) with a suitable cargo
vehicle.

That is the big problem though, literally. Even if you can
quarantee the stage drops in the same spot every time you
still have to get it back. Most realistic first stages for
launch vehicles sized for the most commercially valuable
payload ranges are going to be way, way, way too large to
be transported by air anywhere unless they can fold up
magically like George Jetson's flying car. Ground
transport would be easier but is going to be a sticky
wicket unless the stage lands near a railroad stock yard
every time. Water transport would need a similarly
fortuitous landing locale.

Interestingly, one good option would be a heavy lifting
blimp, which should have the load capacity and range to do
the trick. But, even though there are such on the drawing
boards they don't have any in production yet.

(Henry Spencer) wrote in message ...
In article ,
Niels J=?ISO-8859-1?B?+A==?=rgen Kruse wrote:
Assuming a horizontal velocity component, would it be terrible to take the
1. stage back with something like a CargoLifter?

Not a big problem, if there's a suitable landing spot for the first stage,
and if it's physically compatible (mass, size, etc.) with a suitable cargo
vehicle.

That is the big problem though, literally. Even if you can
quarantee the stage drops in the same spot every time you
still have to get it back. Most realistic first stages for
launch vehicles sized for the most commercially valuable
payload ranges are going to be way, way, way too large to
be transported by air anywhere unless they can fold up
magically like George Jetson's flying car. Ground
transport would be easier but is going to be a sticky
wicket unless the stage lands near a railroad stock yard
every time. Water transport would need a similarly
fortuitous landing locale.

Interestingly, one good option would be a heavy lifting
blimp, which should have the load capacity and range to do
the trick. But, even though there are such on the drawing
boards they don't have any in production yet.

Alright, back to powered flybacks for first stages. Are jet engines
worth the trouble of extra systems? Could one of several main rocket
engines be used frugally to keep the stage up to speed during its
return flight, and some or all of the weight that would've gone to jet
engines be used for additional rocket fuel?

In *very* broad terms -

Specific Impulse Thrust/weight
Rockets ~ 400 sec ~ 50:1
Jets ~ 4000 sec ~ 5:1

For fly-back, rockets are just too thirsty. Its no trouble to have a small
supplementary rocket (high T/W), or a few left on out of a cluster used at
launch, but lugging the extra propellant to many thousands of mph is
prohibitive.

For fly-back, jets are just too heavy (bear in mind that they need ducting,
& create extra drag during launch or incur the added mass of pop-out mounts).

That leaves 3 options
- a downrange landing field with fly-home bolt-on jets
- reuse from downrange launch pad (practical for heavy sustained ops)
- jets that "pay their way" by operating in the first 50 sec of launch
ie while subsonic in dense atmosphere.

Alright, back to powered flybacks for first stages. Are jet engines
worth the trouble of extra systems? Could one of several main rocket
engines be used frugally to keep the stage up to speed during its
return flight, and some or all of the weight that would've gone to jet
engines be used for additional rocket fuel?

In *very* broad terms -

Specific Impulse Thrust/weight
Rockets ~ 400 sec ~ 50:1
Jets ~ 4000 sec ~ 5:1

For fly-back, rockets are just too thirsty. Its no trouble to have a small
supplementary rocket (high T/W), or a few left on out of a cluster used at
launch, but lugging the extra propellant to many thousands of mph is
prohibitive.

For fly-back, jets are just too heavy (bear in mind that they need ducting,
& create extra drag during launch or incur the added mass of pop-out mounts).

That leaves 3 options
- a downrange landing field with fly-home bolt-on jets
- reuse from downrange launch pad (practical for heavy sustained ops)
- jets that "pay their way" by operating in the first 50 sec of launch
ie while subsonic in dense atmosphere.

On Dec 6, 2003, at 7:08 PM, Christopher M. Jones wrote:

That is the big problem though, literally. Even if you can
quarantee the stage drops in the same spot every time you
still have to get it back.

That's certainly one selling point for SSTO RLV, yeah?
It returns to the launch site as part of the flight profile.

Hopefully when the Prez announces the "Giant Crawl Back"...
we'll get back into the Heavy Lift business again.

Not that my opinion matters, but... here's what I'm hoping for:

1) 100 tons to LEO. (Saturn V class payload)
2) SSTO, Trivially Reusable "Booster". (Implies wings; Sorry)
3) If you want to put an OSP that can seat 10 on top of it, fine.
4) The OSP should be able to survive a catastrophic booster failure.

Aloha mai Nai`a!
--
"Please have your Internet License http://kapu.net/~mjwise/
and Usenet Registration handy..."

On Dec 6, 2003, at 7:08 PM, Christopher M. Jones wrote:

That is the big problem though, literally. Even if you can
quarantee the stage drops in the same spot every time you
still have to get it back.

That's certainly one selling point for SSTO RLV, yeah?
It returns to the launch site as part of the flight profile.

Hopefully when the Prez announces the "Giant Crawl Back"...
we'll get back into the Heavy Lift business again.

Not that my opinion matters, but... here's what I'm hoping for:

1) 100 tons to LEO. (Saturn V class payload)
2) SSTO, Trivially Reusable "Booster". (Implies wings; Sorry)
3) If you want to put an OSP that can seat 10 on top of it, fine.
4) The OSP should be able to survive a catastrophic booster failure.

Aloha mai Nai`a!
--
"Please have your Internet License http://kapu.net/~mjwise/
and Usenet Registration handy..."