DV Calculation clarification (rocket booster)

  • #1
30
4

Summary:

When calculating the dV available from a rocket booster, is the ISP always multiplied by 9.81 to get the exhaust velocity?
When calculating the dV available from a rocket booster, the below calculation is used:

(ISP . g) . ln(Mass when full/Mass when empty)

Is 'g' always equal to 9.81 in this equation, or do you use the actual gravitational acceleration that the booster will experience, at it's given altitude, to calculate the exhaust velocity?
 

Answers and Replies

  • #2
494
196
Summary:: When calculating the dV available from a rocket booster, is the ISP always multiplied by 9.81 to get the exhaust velocity?

When calculating the dV available from a rocket booster, the below calculation is used:

(ISP . g) . ln(Mass when full/Mass when empty)

Is 'g' always equal to 9.81 in this equation, or do you use the actual gravitational acceleration that the booster will experience, at it's given altitude, to calculate the exhaust velocity?
Constant value of 1kgf (9.806650) is used. The question about ISP is the classical example of the troubles associated with the non-metric units. Historically, ISP measured in seconds was useful because it can be derived from thrust and fuel flow rates expressed in both metric and imperial units, without changing the formula.
 
  • Like
Likes Dinoduck94
  • #3
cjl
Science Advisor
1,864
437
As trurle said, it's just a unit conversion, so you just use 32.2 if you want your result in ft/s or 9.8 if you want your result in m/s. It doesn't matter at all what conditions the rocket is experiencing.
 

Related Threads on DV Calculation clarification (rocket booster)

  • Last Post
Replies
9
Views
17K
Replies
1
Views
849
  • Last Post
Replies
8
Views
3K
  • Last Post
Replies
1
Views
3K
Replies
16
Views
4K
  • Last Post
Replies
16
Views
5K
  • Last Post
Replies
8
Views
957
  • Last Post
Replies
1
Views
636
Replies
1
Views
2K
Top