Elon Musk's SpaceX to build 'Grasshopper' hover-rocket

A couple of suggestions for the reusable version of the Falcon 9.
First, model it on the DC-X. In the SpaceX video of the proposed
reusable launcher the first and second stages have the same straight
sides of the expendable versions. But having sloping sides helps to
protect the sides of the vehicle during reentry as well as increasing
aerodynamic stability during reentry.
Note that as long as the cross-section remains circular for a conical
shaped stage you should still get the high tankage ratio that obtains
for cylindrical tanks:

Space Access Update #91 2/7/00.
The Last Five Years: NASA Gets Handed The Ball, And Drops It.
"...part of L-M X-33's weight growth was the "multi-
lobed" propellant tanks growing considerably heavier than promised.
Neither Rockwell nor McDonnell-Douglas bid these; both used proven
circular-section tanks. X-33's graphite-epoxy "multi-lobed" liquid
hydrogen tanks have ended up over twice as heavy relative to the
weight of propellant carried as the Shuttle's 70's vintage aluminum
circular-section tanks - yet an X-33 tank still split open in test
last fall. Going over to aluminum will make the problem worse; X-
33's aluminum multi-lobed liquid oxygen tank is nearly four times as
heavy relative to the weight of propellant carried as Shuttle's
aluminum circular-section equivalent."
http://www.space-access.org/updates/sau91.html

The McDonnell-Douglas version mentioned there was the scaled up DC-X.
There are a couple of ways this DC-X styled Falcon 9 could be
implemented. As this is to be a multi-stage launcher, you could have
each stage have the same sloping sides as the DC-C. Then each stage
would have the shape of a truncated cone, a frustum, and when stacked
one on top another the vehicle would have the shape of a single cone.
However, I prefer another method. It is known that you can increase
your payload using parallel staging with cross-feed fueling. Indeed
SpaceX intends to increase the payload of its Falcon Heavy launcher
using this method. Then another method for this reusable Falcon 9
would have each stage in the shape of a full cone, but the second
stage instead of being placed on top of the first stage would be
placed along side of it in parallel fashion.
In addition to increasing the payload this would have an another key
advantage. The high mass ratio of the Falcon 9 first stage, above 20
to 1, means that if it had high efficiency engines such as the NK-33
or RD-180 instead of the rather low efficiency Merlin 1C it would have
SSTO capability. However, because of the high investment of SpaceX in
the Merlin engines they no doubt are committed to its use.
But a key fact is that IF you have altitude compensation then even a
low efficiency, i.e., low chamber pressure, engine can achieve high
vacuum Isp while still providing good performance at sea level.
Methods of altitude compensation such as the aerospike have been
studied since the 60's. Then SpaceX could provide their DC-X styled
Falcon 9 stages with altitude compensation to give their stages SSTO
capability while still using the Merlin engines.
Then these SSTO stages could serve as low cost launchers for smaller
payloads, including being used for private, manned orbital vehicles.

The second model for the reusable Falcon 9 stages would be on the
ESA's proposed Intermediate eXperimental Vehicle (IXV):

Article:
Europe Aims to Launch Robotic Mini-Shuttle By 2020.
Rob Coppinger, SPACE.com ContributorDate: 13 June 2011 Time: 02:58 PM
ET
http://www.space.com/11948-robot-spa...hing-2020.html

This does not use the powered landing of the DC-X but rather uses a
glided landing via its lifting body shape. SpaceX does not like the
use of wings for landing because of the extra weight. But this design
would not have wings. It would have larger thermal protection weight
because the horizontal underside would have to be covered, whereas in
the DC-X mode only the base has to be covered. However, it would make
up for this in not requiring fuel for the powered landing.
In this case because the stages would have to maintain the aerodynamic
shape, they could not be stacked as for serial staging. Parallel
staging would have to be used. Once again this means the separate
stages could be used as SSTO's.


Bob Clark

On Oct 2, 7:17*pm, Robert Clark wrote:
*A couple of suggestions for the reusable version of the Falcon 9.
...

The second model for the reusable Falcon 9 stages would be on the
ESA's proposed Intermediate eXperimental Vehicle (IXV):

Article:
Europe Aims to Launch Robotic Mini-Shuttle By 2020.
Rob Coppinger, SPACE.com ContributorDate: 13 June 2011 Time: 02:58 PM
EThttp://www.space.com/11948-robot-spa...hing-2020.html



That Space.com link should be:

Europe Aims to Launch Robotic Mini-Shuttle By 2020.
http://www.space.com/11948-robot-spa...hing-2020.html

Bob Clark

On Oct 2, 7:17*pm, Robert Clark wrote:
*A couple of suggestions for the reusable version of the Falcon 9.
First, model it on the DC-X. In the SpaceX video of the proposed
reusable launcher the first and second stages have the same straight
sides of the expendable versions. But having sloping sides helps to
protect the sides of the vehicle during reentry as well as increasing
aerodynamic stability during reentry.
Note that as long as the cross-section remains circular for a conical
shaped stage you should still get the high tankage ratio that obtains
for cylindrical tanks:

Space Access Update #91 2/7/00.
The Last Five Years: NASA Gets Handed The Ball, And Drops It.
"...part of L-M X-33's weight growth was the "multi-
lobed" propellant tanks growing considerably heavier than promised.
Neither Rockwell nor McDonnell-Douglas bid these; both used proven
circular-section tanks. X-33's graphite-epoxy "multi-lobed" liquid
hydrogen tanks have ended up over twice as heavy relative to the
weight of propellant carried as the Shuttle's 70's vintage aluminum
circular-section tanks - yet an X-33 tank still split open in test
last fall. Going over to aluminum will make the problem worse; X-
33's aluminum multi-lobed liquid oxygen tank is nearly four times as
heavy relative to the weight of propellant carried as Shuttle's
aluminum circular-section equivalent."http://www.space-access.org/updates/sau91.html

The McDonnell-Douglas version mentioned there was the scaled up DC-X.
There are a couple of ways this DC-X styled Falcon 9 could be
implemented. As this is to be a multi-stage launcher, you could have
each stage have the same sloping sides as the DC-C. Then each stage
would have the shape of a truncated cone, a frustum, and when stacked
one on top another the vehicle would have the shape of a single cone.
However, I prefer another method. It is known that you can increase
your payload using parallel staging with cross-feed fueling. Indeed
SpaceX intends to increase the payload of its Falcon Heavy launcher
using this method. Then another method for this reusable Falcon 9
would have each stage in the shape of a full cone, but the second
stage instead of being placed on top of the first stage would be
placed along side of it in parallel fashion.
In addition to increasing the payload this would have an another key
advantage. The high mass ratio of the Falcon 9 first stage, above 20
to 1, means that if it had high efficiency engines such as the NK-33
or RD-180 instead of the rather low efficiency Merlin 1C it would have
SSTO capability. However, because of the high investment of SpaceX in
the Merlin engines they no doubt are committed to its use.
But a key fact is that IF you have altitude compensation then even a
low efficiency, i.e., low chamber pressure, engine can achieve high
vacuum Isp while still providing good performance at sea level.
Methods of altitude compensation such as the aerospike have been
studied since the 60's. Then SpaceX could provide their DC-X styled
Falcon 9 stages with altitude compensation to give their stages SSTO
capability while still using the Merlin engines.
Then these SSTO stages could serve as low cost launchers for smaller
payloads, including being used for private, manned orbital vehicles.

The second model for the reusable Falcon 9 stages would be on the
ESA's proposed Intermediate eXperimental Vehicle (IXV):

Article:
Europe Aims to Launch Robotic Mini-Shuttle By 2020.
Rob Coppinger, SPACE.com ContributorDate: 13 June 2011 Time: 02:58 PM
EThttp://www.space.com/11948-robot-spa...hing-2020.html

This does not use the powered landing of the DC-X but rather uses a
glided landing via its lifting body shape. SpaceX does not like the
use of wings for landing because of the extra weight. But this design
would not have wings. It would have larger thermal protection weight
because the horizontal underside would have to be covered, whereas in
the DC-X mode only the base has to be covered. However, it would make
up for this in not requiring fuel for the powered landing.
In this case because the stages would have to maintain the aerodynamic
shape, they could not be stacked as for serial staging. Parallel
staging would have to be used. Once again this means the separate
stages could be used as SSTO's.


Other possible methods to make the Falcon 9 reusable might be to use
the "parashield" idea of the Dr. David Akin or the inflatable heat
shield NASA is investigating. These might make the reusable Falcon 9
easier and quicker to implement since the usual cylindrical shaped
stages could be used:

Phoenix: A Low-Cost Commercial Approach to the Crew Exploration
Vehicle.
http://www.nianet.org/rascal/forum20..._umd_paper.pdf

"Figure 5.9-1: Phoenix ParaShield in stowed and deployed
configurations."
http://oi51.tinypic.com/14e9vd4.jpg

Another advantage of the parashield is that it can also serve as a
parachute once the vehicle has passed through reentry.

And for NASA's inflatable heat shield:

NASA Launches New Technology: An Inflatable Heat Shield.
UPDATE: 08.17.09
http://www.nasa.gov/topics/aeronauti...ures/irve.html

See the video on this page describing the inflatable heat shield.


Bob Clark

I pictured it landing horizontally, not vertically. They'll have to be
very careful with centre of gravity.

On Oct 2, 7:17*pm, Robert Clark wrote:
*A couple of suggestions for the reusable version of the Falcon 9.
First, model it on the DC-X. In the SpaceX video of the proposed
reusable launcher the first and second stages have the same straight
sides of the expendable versions. But having sloping sides helps to
protect the sides of the vehicle during reentry as well as increasing
aerodynamic stability during reentry.
Note that as long as the cross-section remains circular for a conical
shaped stage you should still get the high tankage ratio that obtains
for cylindrical tanks:

...
The second model for the reusable Falcon 9 stages would be on the
ESA's proposed Intermediate eXperimental Vehicle (IXV):

Article:
Europe Aims to Launch Robotic Mini-Shuttle By 2020.
Rob Coppinger, SPACE.com ContributorDate: 13 June 2011 Time: 02:58 PM
EThttp://www.space.com/11948-robot-spa...hing-2020.html

This does not use the powered landing of the DC-X but rather uses a
glided landing via its lifting body shape. SpaceX does not like the
use of wings for landing because of the extra weight. But this design
would not have wings. It would have larger thermal protection weight
because the horizontal underside would have to be covered, whereas in
the DC-X mode only the base has to be covered. However, it would make
up for this in not requiring fuel for the powered landing.
In this case because the stages would have to maintain the aerodynamic
shape, they could not be stacked as for serial staging. Parallel
staging would have to be used. Once again this means the separate
stages could be used as SSTO's.


Another possible lifting-body shape for reusable Falcon 9 stages might
be of the Japanese HYFLEX hypersonic test vehicle:

Hypersonic Flight Experiment "HYFLEX".
http://www.jaxa.jp/projects/rockets/hyflex/index_e.html

HYFLEX.
http://www.rocket.jaxa.jp/fstrc/0c02.html

This was successfully tested all the way back in 1996 at a Mach 15
reentry speed.
It's roughly cylindrical shape would mean you would lose a relatively
small degree on the mass efficiency of cylindrically shaped tanks.
However, rather than redesigning the tanks you might want to just use
a composite aeroshell on the usual Falcon 9 stages. A conical
aeroshell for example was used on the DC-X.
This would make the reusable Falcon 9 more quickly and easily to be
implemented. The mass of the aeroshell though would contribute to the
mass lost from payload.
As with the above cases, if used with altitude compensating nozzles
on the Merlins or with existing high efficiency engines with just
their standard nozzles, these HYFLEX-shaped stages could also be
SSTO's.


Bob Clark