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Saturday, November 29, 2014

A half-size Ariane for manned spaceflight.

Copyright 2014 Robert Clark

 The current agreed  upon design for the Ariane 6 is to use a slightly reduced in size Ariane 5 core with strap-on solid boosters about half-size to the solids used on the Ariane 5:

Ariane 6.

   I believe this is a preferred solution for the Ariane 6 than the version using all solid lower stages. For one thing, if SpaceX succeeds in producing a reusable first stage, then ESA can keep pace by making the core stage of the Ariane 6 reusable.

 My ideal solution however would have used two to three Vulcain engines on the core stage. This would have an additional advantage of being able to be used as a manned launcher with no solids attached:

Friday, March 29, 2013
The Coming SSTO's: multi-Vulcain Ariane.
Copyright 2013 Robert Clark
http://exoscientist.blogspot.com/2013/03/the-coming-sstos-multi-vulcain-ariane.html



Single-Stage To Orbit Case. Still we can get a manned launcher retaining a single Vulcain II on the core and shrinking the size of the stage, to half-size. As discussed in the "The Coming SSTO's: multi-Vulcain Ariane" post, the propellant mass of the Ariane 5G core is 158,000 kg, with a 12,000 kg dry mass. We may remove a forward skirt called the "JAVE" used to attach the solids to the Ariane 5. This massed 1,700 kg bringing the dry mass down to 10,300 kg. The propellant tank on the Ariane 5G weighed 4,400 kg. So half-size this will weigh 2,200 kg, bringing the dry mass down to 8,100  kg. 
 In Dr. John Schilling's Launch Performance Calculator, enter in now also 79,000 kg for the propellant mass, 1,350 kN for the vacuum thrust and 434 s for the vacuum Isp. Select Kourou as the launch site with a launch inclination of 5.2 degrees, to match the launch site latitude. The "Restartable Upper Stage" option should be checked "No" even for a single stage, otherwise the payload will be reduced. Then the calculator gives:


Mission Performance:
Launch Vehicle:  User-Defined Launch Vehicle
Launch Site:  Guiana Space Center (Kourou)
Destination Orbit:  185 x 185 km, 5 deg
Estimated Payload:  2528 kg
95% Confidence Interval:  1064 - 4248 kg
"Payload" refers to complete payload system weight, including any necessary payload attachment fittings or multiple payload adapters
This is an estimate based on the best publicly-available engineering and performance data, and should not be used for detailed mission planning. Operational constraints may reduce performance or preclude this mission.

  This payload of 2,500 kg is for a single stage to orbit vehicle. As discussed in the blog post "Budget Moon flights: lightweight crew capsule", this may be sufficient for a 3-person capsule to LEO. For instance the Cygnus capsule given life support may fit within this size range. I have discussed though an SSTO reaches its best performance when using altitude compensation: "Altitude compensation attachments for standard rocket engines, and applications".

 By using altitude compensation the vacuum Isp can be raised to 466 s and the vacuum thrust to 1,350 kN*(466/434) = 1,450 kN. Schilling's calculator now gives a result of: 

Mission Performance:                  
Launch Vehicle:  User-Defined Launch Vehicle
Launch Site:  Guiana Space Center (Kourou)
Destination Orbit:  185 x 185 km, 5 deg
Estimated Payload:  4544 kg
95% Confidence Interval:  2894 - 6480 kg
"Payload" refers to complete payload system weight, including any necessary payload attachment fittings or multiple payload adapters
This is an estimate based on the best publicly-available engineering and performance data, and should not be used for detailed mission planning. Operational constraints may reduce performance or preclude this mission.



 As discussed in the "altitude compensation" blog post though characteristics of how the Schilling calculator makes its estimates may make it less accurate in a scenario using altitude compensation. A more accurate analysis that varies the Isp from ground to orbit may be needed in this case.

Two-Stage To Orbit Case.

 We can get a higher payload manned launcher by making it TSTO. We'll use the cryogenic upper stage the Ariane H10-3. The Astronautix page gives it a gross mass of 12,310 kg and dry mass of 1,570 kg, for a propellant mass of 10,740 kg. The Isp is listed as 446 s with a vacuum thrust of 62.70 kN. However, this extra mass for the upper stage would mean the single Vulcain II on the core could not loft it.


 Then we'll reduce the propellant load in the core stage. It might also work to run the Vulcain at some percentage above the rated thrust, or use a varied mixture ratio at launch compared to high altitude. But using a reduction of the propellant load method, we'll lessen the propellant in the first stage by the mass of the upper stage, so by 12,310 kg. This brings the propellant load of the first stage to 66,690 kg. There is about a 35 to 1 ratio of propellant to tank mass so this will reduce the tank mass of the first stage by 12,310 kg/35 =350 kg. Then the dry mass of the core becomes 7,750 kg.  Then the calculator gives:


Mission Performance:
Launch Vehicle:  User-Defined Launch Vehicle
Launch Site:  Guiana Space Center (Kourou)
Destination Orbit:  185 x 185 km, 5 deg
Estimated Payload:  4891 kg
95% Confidence Interval:  3970 - 5982 kg
"Payload" refers to complete payload system weight, including any necessary payload attachment fittings or multiple payload adapters
This is an estimate based on the best publicly-available engineering and performance data, and should not be used for detailed mission planning. Operational constraints may reduce performance or preclude this mission.


 We'll also estimate the payload for the altitude compensation case. Again take the first case vacuum thrust as 1,450 kN and the vacuum Isp as 466 s. But also improve the thrust and Isp for the upper stage, The thrust becomes 62.70 *(466/446) =  65.5 kN, with vacuum Isp also 466 s. Then the Schilling calculator gives:


Mission Performance:
Launch Vehicle:  User-Defined Launch Vehicle
Launch Site:  Guiana Space Center (Kourou)
Destination Orbit:  185 x 185 km, 5 deg
Estimated Payload:  6075 kg
95% Confidence Interval:  5016 - 7334 kg

"Payload" refers to complete payload system weight, including any necessary payload attachment fittings or multiple payload adaptersThis is an estimate based on the best publicly-available engineering and performance data, and should not be used for detailed mission planning. Operational constraints may reduce performance or preclude this mission.

 Again however this estimate for the altitude compensation case would have to be confirmed with more accurate estimation methods.


  Bob Clark

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