payload2leo.py

# Neph adapted this from Momo
# https://repl.it/repls/WellwornBowedDemos

# Import packages
import numpy as np

# Multi-stage deltaV calculator. All arguments must be lists of the same length except the int 'payload'
def getdV(isp, wet, dry, payload):
  dV = 0
  wet.append(0)
  for i in range(len(isp)):
    dV += isp[i] * np.log((sum(wet[i:])+payload) / (dry[i]+sum(wet[i+1:])+payload))
  return dV * 9.8

# Payload calculator
def getPayload(isp, wet, dry, dV2leo):
  dV = getdV(isp, wet, dry, 0)
  if dV < dV2leo:
    # oof
    return -1
  else:
    # Payload mass
    payload = 0
    # Iteration variables
    i = 1
    lastSign = 1
    # Iterate until the dV equation is solved
    while np.abs(dV-dV2leo) > 1:
      # This helps us close in on a solution
      sign = np.sign(dV-dV2leo)
      if sign != lastSign: i *= 2
      # Change payload mass
      payload += sign*100/i
      # Recalculate
      dV = getdV(isp, wet, dry, payload)
      # Iterate
      lastSign = sign
  # Solution!
  return payload

# Run the thing
while True:
  try:
    # Set up parameter lists
    isp = []
    wet = []
    dry = []
    # Get stages
    moreStages = True
    stage = 1
    while True:
      # Get first-stage boosters
      if stage == 1:
        print("Are there boosters? (If so, they must have the same engines as the first stage for this calculator to work) [Y/n]: ")
        if input() != 'n':
          print("Input first stage/booster engine isp (seconds):")
          ISP = float(input())
          print("Input engine fuel consumption rate (tons/sec):")
          rate = float(input())
          print("Input number of first stage engines:")
          enginesFirst = float(input())
          print("Input first stage total mass (tons):")
          wetFirst = float(input())
          print("Input first stage fuel mass (tons):")
          fuelFirst = float(input())
          dryFirst = wetFirst - fuelFirst
          print("Input number of booster engines:")
          enginesBoosters = float(input())
          print("Input booster total mass (tons):")
          wetBoosters = float(input())
          print("Input booster fuel mass (tons):")
          dryBoosters = wetBoosters - float(input())
          # Calculate how long it takes for boosters to burn dry
          t = (wetBoosters - dryBoosters)/rate/enginesBoosters
          firstFuelConsumedWithBoosters = rate*t*enginesFirst
          if firstFuelConsumedWithBoosters > fuelFirst:
            raise Exception("Your boosters finish after your first stage does. This calculator cannot handle that lift vehicle architecture.")
          # Calculate the booster+first stage "stage"
          isp.append(ISP)
          wet.append(wetBoosters + firstFuelConsumedWithBoosters)
          dry.append(dryBoosters)
          # Caculate the remainder of the first stage "stage"
          isp.append(ISP)
          wet.append(wetFirst - firstFuelConsumedWithBoosters)
          dry.append(dryFirst)
          # More stages?
          print("Are there more stages? [y/N]")
          if input() == 'y':
            stage += 1
          else:
            break
      # Get stage parameters
      print(f"Input stage {stage} engine isp (seconds): ")
      isp.append(float(input()))
      print(f"Input stage {stage} total mass (tons): ")
      wet.append(float(input()))
      print(f"Input stage {stage} fuel mass (tons): ")
      dry.append(wet[-1] - float(input()))
      # More stages?
      print("Are there more stages? [y/N]")
      if input() == 'y':
        stage += 1
      else:
        break
    # Okay, let's get a move on
    print("Without payload, you have", str(int(getdV(isp, wet, dry, 0))), "m/s of delta V.")
    # Will we go to space?
    payload = getPayload(isp, wet, dry, 2300.0)
    if payload == -1:
      # oof
      print("You will not go to space today. :(")
    else:
      # yay
      print("With a very high t/w ratio, perfect piloting and no drag, you can lift", str(int(payload)), "tons to LEO.\nDon't abuse the drag bug!")
      # What would a realistic payload be?
      realistic = getPayload(isp, wet, dry, 3000.0)
      if realistic == -1:
        print("Realistically, you'll probably have a hard time getting anything to orbit.")
      else:
        print("Realistically, you'll probably be able to get", str(int(realistic)), "tons to orbit.")
    # Move it along now
    print("\nPress Enter to continue.")
    input()

  except ValueError:
    print("Please give me numbers.")

  except Exception as error:
    print(error)