Author Topic: Alpha biased steering  (Read 1341 times)

Offline fatjohn1408

  • Full Member
  • ***
  • Posts: 316
  • Liked: 15
  • Likes Given: 13
Alpha biased steering
« on: 04/14/2014 05:40 PM »
Could anyone please specify what Alpha biased angle-of-attack steering entails, how large the bending moment becomes due to it, how much lift is generated (that is what I presume is the benefit), how much of a performance gain is received from this, etc.

From the Atlas V User manual:
Quote
For Atlas V 401 or 402 configurations, after reaching 24,380 m (80,000 ft) until 33,530 m (110,000 ft), an
alpha-bias angle-of-attack steering technique is used to improve performance while maintaining
aerodynamic loading within acceptable limits.
Closed-loop guidance steering is enabled at the end of alpha-biased steering. For all Atlas V 400 series LVs
with SRBs, the zero-alpha/zero-beta attitude is maintained until 6 seconds after the initial SRB jettison when
closed-loop guidance steering is enabled. The SRB jettison sequence is initiated after SRB burnout. SRBs 1
and 2, if applicable, are jettisoned at a predetermined time dependent upon a dynamic pressure constraint.
SRB 3 is jettisoned 1.5 seconds later, if applicable.

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 32441
  • Cape Canaveral Spaceport
  • Liked: 11187
  • Likes Given: 331
Re: Alpha biased steering
« Reply #1 on: 04/14/2014 06:19 PM »
Could anyone please specify what Alpha biased angle-of-attack steering entails, how large the bending moment becomes due to it, how much lift is generated (that is what I presume is the benefit), how much of a performance gain is received from this, etc.

It using predicted winds aloft to generate a trajectory that minimize loads.  If the guidance was closed loop, the vehicle would "fight' against the winds and fly into them, which will induce loads. 
The rest is how I think it works.
Alpha biased angle-of-attack steering flies at a specific alpha for the predicted/measured winds aloft and takes into account the inefficiencies that this will cause in performance.  The benefit is not lift or increase performance but increased launch probability.

Tags: