Stratolaunch: General Company and Development Updates and Discussions

[MP99]

  Liquid fuel rocket design has been optimized since the beginning for almost purely longitudinal forces on the tank and stage structures.  To make a liquid fuel rocket structurally capable of hanging sideways would vastly increase its dry mass fraction. 

The above assertion is false. Most launch vehicles are designed to handle longitudinal loads.

No, it is true, launch vehicles are not designed to handle the lateral loads such as those that will be found on Stratolaunch.  Especially those from being suspended horizontally, and then including propellant.

I do wonder whether Falcon will be dry at takeoff, then fuelled up from tanks in the twin fuselages (they look large enough) before launch.

It would at least reduce the lateral loads on Falcon during takeoff. I'm assuming lateral accelerations would be lower during flight.

cheers, Martin

[Jim]

It would at least reduce the lateral loads on Falcon during takeoff. I'm assuming lateral accelerations would be lower during flight.

when have you experienced more accelerations on a plane, takeoff or during level flight?  Have you ever been on a flight where they put on the seatbelt light during cruise?

[Danderman]

  Liquid fuel rocket design has been optimized since the beginning for almost purely longitudinal forces on the tank and stage structures.  To make a liquid fuel rocket structurally capable of hanging sideways would vastly increase its dry mass fraction. 

The above assertion is false. Most launch vehicles are designed to handle longitudinal loads.

No, it is true, launch vehicles are not designed to handle the lateral loads such as those that will be found on Stratolaunch.  Especially those from being suspended horizontally, and then including propellant.

All I can do in response is provide data.

[Jim]

  Liquid fuel rocket design has been optimized since the beginning for almost purely longitudinal forces on the tank and stage structures.  To make a liquid fuel rocket structurally capable of hanging sideways would vastly increase its dry mass fraction. 

The above assertion is false. Most launch vehicles are designed to handle longitudinal loads.

No, it is true, launch vehicles are not designed to handle the lateral loads such as those that will be found on Stratolaunch.  Especially those from being suspended horizontally, and then including propellant.

All I can do in response is provide data.

2 g's is not a significant load.

And does not envelope "those that will be found on Stratolaunch.  Especially those from being suspended horizontally, and then including propellant."

[HMXHMX]

  Liquid fuel rocket design has been optimized since the beginning for almost purely longitudinal forces on the tank and stage structures.  To make a liquid fuel rocket structurally capable of hanging sideways would vastly increase its dry mass fraction. 

The above assertion is false. Most launch vehicles are designed to handle longitudinal loads.

No, it is true, launch vehicles are not designed to handle the lateral loads such as those that will be found on Stratolaunch.  Especially those from being suspended horizontally, and then including propellant.

All I can do in response is provide data.

You are looking at the loads the spacecraft needs to address, not the booster.  These are powered flight loads; carriage loads are handling loads unrelated to powered flight conditions.

The Orbiter had similar distinctions.  Landing (and abort landing) loads (something you don't design for in an ELV) were big drivers in spacecraft design but are unrelated to powered ascent flight conditions.

[Jim]

  Liquid fuel rocket design has been optimized since the beginning for almost purely longitudinal forces on the tank and stage structures.  To make a liquid fuel rocket structurally capable of hanging sideways would vastly increase its dry mass fraction. 

The above assertion is false. Most launch vehicles are designed to handle longitudinal loads.

No, it is true, launch vehicles are not designed to handle the lateral loads such as those that will be found on Stratolaunch.  Especially those from being suspended horizontally, and then including propellant.

All I can do in response is provide data.

You are looking at the loads the spacecraft needs to address, not the booster.  These are powered flight loads; carriage loads are handling loads unrelated to powered flight conditions.

The Orbiter had similar distinctions.  Landing (and abort landing) loads (something you don't design for in an ELV) were big drivers in spacecraft design but are unrelated to powered ascent flight conditions.

Pegasus loads for spacecraft are much higher.

[HMXHMX]

  Liquid fuel rocket design has been optimized since the beginning for almost purely longitudinal forces on the tank and stage structures.  To make a liquid fuel rocket structurally capable of hanging sideways would vastly increase its dry mass fraction. 

The above assertion is false. Most launch vehicles are designed to handle longitudinal loads.

No, it is true, launch vehicles are not designed to handle the lateral loads such as those that will be found on Stratolaunch.  Especially those from being suspended horizontally, and then including propellant.

All I can do in response is provide data.

You are looking at the loads the spacecraft needs to address, not the booster.  These are powered flight loads; carriage loads are handling loads unrelated to powered flight conditions.

The Orbiter had similar distinctions.  Landing (and abort landing) loads (something you don't design for in an ELV) were big drivers in spacecraft design but are unrelated to powered ascent flight conditions.

Pegasus loads for spacecraft are much higher.

Yes.  I was using his Atlas example as the reference.

[Danderman]

  Liquid fuel rocket design has been optimized since the beginning for almost purely longitudinal forces on the tank and stage structures.  To make a liquid fuel rocket structurally capable of hanging sideways would vastly increase its dry mass fraction. 

The above assertion is false. Most launch vehicles are designed to handle longitudinal loads.

No, it is true, launch vehicles are not designed to handle the lateral loads such as those that will be found on Stratolaunch.  Especially those from being suspended horizontally, and then including propellant.

All I can do in response is provide data.

You are looking at the loads the spacecraft needs to address, not the booster.  These are powered flight loads; carriage loads are handling loads unrelated to powered flight conditions.

The Orbiter had similar distinctions.  Landing (and abort landing) loads (something you don't design for in an ELV) were big drivers in spacecraft design but are unrelated to powered ascent flight conditions.

Pegasus loads for spacecraft are much higher.

Are those loads a function of horizontal carriage or the acceleration or shock loads from the SRBs? The Pegasus user guide shows very high shock loads from motor ignition.

[Danderman]

All I have so far from the issue about longitudinal loads are that the loads for a horizontal launch system are *different* from a standard vertical launch - nothing so far indicates that the loads are *greater*. Since the OP claimed that horizontal launch suffers from lower performance due to a requirement that the launch vehicle be more massive to handle the higher loads, I still claim that this is a false assertion.

[go4orbit]

You missed the point.  Longitudinal loads probably are not very different.  Lateral loads are hugely different.  Falcon 9 cannot be plugged in without greatly increasing its structural strength to handle the loads that come from hanging horizontally.  This will kill any performance advantage that would otherwise come from air launch.  Even the old space shuttle flyback booster concepts still had vertical launch.  Stratolaunch does not pass the sniff test.

[MP99]

It would at least reduce the lateral loads on Falcon during takeoff. I'm assuming lateral accelerations would be lower during flight.

when have you experienced more accelerations on a plane, takeoff or during level flight?  Have you ever been on a flight where they put on the seatbelt light during cruise?

Regardless of manoeuvres the pilot may be allowed to fly on a commercial passenger flight, I suspected that a specialist flight could fly with more gentle loadings once into cruise.

However, I take your point about (I presume) turbulence.

cheers, Martin

[Danderman]

You missed the point.  Longitudinal loads probably are not very different.  Lateral loads are hugely different.  Falcon 9 cannot be plugged in without greatly increasing its structural strength to handle the loads that come from hanging horizontally.  This will kill any performance advantage that would otherwise come from air launch.  Even the old space shuttle flyback booster concepts still had vertical launch.  Stratolaunch does not pass the sniff test.

Oops. I was thinking lateral and typed longitudinal.

The above post claims that air launch is not feasible. Interesting.  How about air launch of second stages? You know, fly them up on a first stage, then perform staging when the vehicle is more or less horizontal. Would that work?

[HMXHMX]

You missed the point.  Longitudinal loads probably are not very different.  Lateral loads are hugely different.  Falcon 9 cannot be plugged in without greatly increasing its structural strength to handle the loads that come from hanging horizontally.  This will kill any performance advantage that would otherwise come from air launch.  Even the old space shuttle flyback booster concepts still had vertical launch.  Stratolaunch does not pass the sniff test.

It is perfectly possible to adapt an "existing" vertically-launched LV to an air-launched mode, but you can't do it by simply adding wings, as Stratolaunch currently intends.  You have to support the LV uniformly and carefully by use of the airborne support equipment (ASE) cradle.  That's Dynetics' job in the case of the F5 being proposed.  But the deployment technique is key.  Google "t/LAD" and "patent" for details.

[Danderman]

You missed the point.  Longitudinal loads probably are not very different.  Lateral loads are hugely different.  Falcon 9 cannot be plugged in without greatly increasing its structural strength to handle the loads that come from hanging horizontally.  This will kill any performance advantage that would otherwise come from air launch.  Even the old space shuttle flyback booster concepts still had vertical launch.  Stratolaunch does not pass the sniff test.

It is perfectly possible to adapt an "existing" vertically-launched LV to an air-launched mode, but you can't do it by simply adding wings, as Stratolaunch currently intends.  You have to support the LV uniformly and carefully by use of the airborne support equipment (ASE) cradle.  That's Dynetics' job in the case of the F5 being proposed.  But the deployment technique is key.  Google "t/LAD" and "patent" for details.

We seem to have a difference of opinion here, since the above post implies that a suitable airborne support system would obviate lateral loads on the launcher (this actually makes sense), whereas others here claim that the launcher must be reinforced and thus heavier.

[HMXHMX]

You missed the point.  Longitudinal loads probably are not very different.  Lateral loads are hugely different.  Falcon 9 cannot be plugged in without greatly increasing its structural strength to handle the loads that come from hanging horizontally.  This will kill any performance advantage that would otherwise come from air launch.  Even the old space shuttle flyback booster concepts still had vertical launch.  Stratolaunch does not pass the sniff test.

It is perfectly possible to adapt an "existing" vertically-launched LV to an air-launched mode, but you can't do it by simply adding wings, as Stratolaunch currently intends.  You have to support the LV uniformly and carefully by use of the airborne support equipment (ASE) cradle.  That's Dynetics' job in the case of the F5 being proposed.  But the deployment technique is key.  Google "t/LAD" and "patent" for details.

We seem to have a difference of opinion here, since the above post implies that a suitable airborne support system would obviate lateral loads on the launcher (this actually makes sense), whereas others here claim that the launcher must be reinforced and thus heavier.

In my view, the difference flows from the launch (i.e., air-drop) method.  A winged pull-up – even beginning from a climbing release as intended by SL – imposes significant flight loads, as does carriage on the aircraft (takeoff, rejected takeoff, turbulence, landing, hard landing, etc.).

If you use a stout full length carriage system, and a properly designed LV, it is feasible – but by no means optimal – to start with an existing vertical-launch ELV and, by using the t/LAD approach, end up with a minimally modified air-launched LV that, to the causal observer, looks about the same as the ground-launch version.  But that is not what Stratolaunch seems to be doing, and it will hurt them.

The t/LAD approach has all been worked out in much detail but I am rather limited in what I can say openly.  But we did three drops using the technique, published AIAA papers, and patented it for a good reason.  It works.

But I should stress that the optimal solution is to design the air-launched LV from the ground up.

[Jim]

We seem to have a difference of opinion here, since the above post implies that a suitable airborne support system would obviate lateral loads on the launcher (this actually makes sense), whereas others here claim that the launcher must be reinforced and thus heavier.

If you look at the concept, the airborne support system looks not much different than what Pegasus uses, hence it will required a modified launch vehicle.  That is the whole point here, Statolaunch is not going to be able to use a stock Falcon vehicle.  It is going to be structurally different.

[Danderman]

We seem to have a difference of opinion here, since the above post implies that a suitable airborne support system would obviate lateral loads on the launcher (this actually makes sense), whereas others here claim that the launcher must be reinforced and thus heavier.

If you look at the concept, the airborne support system looks not much different than what Pegasus uses, hence it will required a modified launch vehicle.  That is the whole point here, Statolaunch is not going to be able to use a stock Falcon vehicle.  It is going to be structurally different.

The key point that Gary makes is that the loads that demand a LV redesign are imparted by the winged pull-up.

[Jim]

We seem to have a difference of opinion here, since the above post implies that a suitable airborne support system would obviate lateral loads on the launcher (this actually makes sense), whereas others here claim that the launcher must be reinforced and thus heavier.

If you look at the concept, the airborne support system looks not much different than what Pegasus uses, hence it will required a modified launch vehicle.  That is the whole point here, Statolaunch is not going to be able to use a stock Falcon vehicle.  It is going to be structurally different.

The key point that Gary makes is that the loads that demand a LV redesign are imparted by the winged pull-up.

The carriage loads alone will also demand a redesign.  Standard launch vehicles are not meant to be suspended

[Danderman]

We seem to have a difference of opinion here, since the above post implies that a suitable airborne support system would obviate lateral loads on the launcher (this actually makes sense), whereas others here claim that the launcher must be reinforced and thus heavier.

If you look at the concept, the airborne support system looks not much different than what Pegasus uses, hence it will required a modified launch vehicle.  That is the whole point here, Statolaunch is not going to be able to use a stock Falcon vehicle.  It is going to be structurally different.

The key point that Gary makes is that the loads that demand a LV redesign are imparted by the winged pull-up.

The carriage loads alone will also demand a redesign.  Standard launch vehicles are not meant to be suspended

OK, let me approach the issue a different way: assuming that horizontal carriage requires some sort of modifications for a launch vehicle, what is the mass penalty?

[Jim]

OK, let me approach the issue a different way: assuming that horizontal carriage requires some sort of modifications for a launch vehicle, what is the mass penalty?

Have no way computing the mods needed to convert a vertically launched vehicle to a suspended airlaunch vehicle.