4 Final Report - Emits - ESA

4 Final
Report
As secondary trade-off, the same architecture can be analysed by using HEMPT thrusters with 80 mN
nominal thrust and an Isp of 3000 s.
Following table summarises the results for mass and power
Table 4.5-15: EPS Option 2 Mass Budgets for considered thruster options (figures in kg)
SPT-100 80 mN HEMPT
TOTAL EPS DRY MASS 92.8 103.2
Total Propellant Load 83.0 41.1
TOTAL EPS BOL MASS 175.8 144.3
Table 4.5-16: EPS Option 2 Power Budgets for considered thruster options (figures in W)
SPT-100 80 mN HEMPT
Main Thruster(s) Assembly 2404 5553
PCU & Ancillary 227 464
Total 2632 6017
Total (Including Margins) 2895 6619
Although the system based on HEMPT technology is about 20% lighter, it needs twice the power to be
run. Decreasing power to match the system based on SPT-100 technology could be achieved by:
• either having a 30 mN HEMPT, but thrust times would increase around the nodes,
decreasing the efficiency of firing and thus increasing the quantity of propellant to be used
• or setting the HEMPT at a lower Isp, but being a more massive thruster of SPT for the same
combination of Thrust and Isp, this would not be an option to be considered
The final trade-off solution will depend on spacecraft level trade-off analysis.
EPS for Option 3
The EPS for Option 3 is based on the general architecture envisaged for carrying on AOCS
simulations:
• 8 Main (Attitude) Manoeuvre Thrusters (MMTs) of 30 mN each, Isp of 3000 s;
• 12 Fine Pointing Thruster (FPT) providing down to 0.1 mN of thrust each
The rest of the system has been completed as per Option 3 of Table 4.5-14.
Two MMT options have been considered, namely HEMPT and GIT, while smaller GIT (Isp of 3000 s)
and FEEP (Isp of 6000 s) have been considered as FPT, making four possible combinations for
Option 3. There is little difference in propellant mass (between 574 and 578 kg); the overall EP mass
and power budget are shown in Table 4.5-17and Table 4.5-18, respectively..
Doc. No: GOC-ASG-RP-002 Page 4-71
Issue: 2
Date: 13.05.2009 Astrium GmbH