Extreme Ultraviolet Imaging Spectrometer: proposal level mass estimate

February 10, 1999

 

Introduction

 

The following discussion presents a calculation of the approximate mass of the EIS instrument configurations. The estimates are proposal level calculations where a good margin is assumed and typical values are taken for many of the subsystems. Generally, the line item estimates are good to within about 10-20% with an overall error of 10%. Also, there are usually elements of the design (purge harness, radiator/thermal shielding, very stiff interface bulkheads, instrument pointing legs, additional mechanisms for optics adjustment, etc.) which only become apparent after further study and necessitate further mass margin. The numbers reflect NRL "typical" numbers; the majority of the hardware will be provided by the UK portion of the EIS team and the spreadsheet should be updated to reflect the best UK estimates. A copy of the Excel spreadsheet will be made available for EIS team members to review/modify.

 

General constraints

 

To allow a relevant comparison between the two designs, the following ground rules were generally assumed.

 

  1. an aggressively light-weighted, composite, non-evacuated (purged) structure
  2. filters are mounted in an evacuated cavity
  3. optics are not lightweighted with reasonable aspect ratios
  4. 15 reflector blankets
  5. sunshield assumed to be required
  6. 9kg margin is assumed
  7. LASCO type mounting legs and launch lock are required
  8. both the 2E and 3E are assumed to have a commandable front door located near the front of the instrument.

 

The length of the Cassegrain system was extended by about 20cm to accommodate the clam shell design. Otherwise, the instrument configurations are essentially as described in the NRL proposal and the science team report.

 

 

Mass calculation summary

 

The EIS mass estimate was carried out by dividing the instrument into about 20 subassemblies. The mass of each subassembly was then derived using a simple mass model of each significant subassembly component. The calculated mass of the subassembly was compared to the mass of a previously constructed mechanism where possible. An additional 15% margin (9kg) was added onto the instrument; this margin is actually somewhat less than the 20% margin typically recommended for this stage of the program. Given the overall heritage of some of the subassemblies, we feel that this is not an unreasonable approach.

 

Table 1: pre-phase A EIS mass calculation results.

Instrument design

calculated mass

full size two element EIS

72.6kg

full size three element EIS

59.7kg

0.82 scaled, two element EIS

59.1kg

 

The calculated mass of essentially three instrument configurations is shown in Table 1. Tables 2 and 3 show the individual subassembly breakdowns. Table 4 presents the calculated mass of a scaled, two element EIS. Sensible "first order" scaling factors were applied to the various components. The linear dimensions of the EIS were scaled by factor of 0.82 which allowed the mass budget to be realized. The implied instrument would have the equivalent f# but the spatial resolution would be 2.27 arcseconds/pixel; the spectral dispersion would be equivalent to a 1.23m Rowland circle. Further mass margin could be most easily achieved in the case of the Cassegrain by a modest decrease in the size of the spectrometer with the resulting reduction in spectral dispersion or an overall size decrease.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TRENDY mass estimate (preliminary 2/5/99)

item

mass (kg)

basis for estimate

electronics box

11

based on single string compact PCI box
   

available from Lockheed Martin
   

9 kg for the populated box and cards
   

2 kg for thermal/mechanical hardware
   

CPU is the RAD-6000, 32bit 30MHz
   

RISC processor
   

Box has slots for 8 3U format cards

structure

25

composite structure
   

10kg devoted to envelope
   

15kg for stiffening ribs and internal bulkheads

door mechanism

1.4

based on LASCO door mechanism

camera

1.5

typical for current technology

primary mirror

2.6

not light weighted, typical aspect ratio
   

16x16x4=1024cm^3
   

Zerodur density 2.56g/cm^3

mirror mount

0.5

typical

scan mechanism

2

scaled from SUMER mechanism mass

grating

2.2

16x16x4=1024cm^3
   

fused silica density of 2.2g/cm^3

grating mount

0.5

typical

grating focus mech.

0.8

based on HRTS focus mechanism

shutter

0.3

typical for direct drive shutter

slit/slot mechanism

0.5

typical for a wheel mechanism

filter frames

0.2

typical thickness and stiffness

evacuated cavity

2.5

18x18x5 evacuated cavity
   

3mm thick
   

heavy duty hinges, paraffin actuators
   

stiffening ribs, gauge and valve

MLI

4

15 layer blankets with alternating mesh
   

liner and cover, mounting hardware

sunshield

0.9

LASCO type

cables

4

scaled from LASCO cables

mounting legs

2

typical for LASCO type

launch lock

1

typical for LASCO type

slit focus mechanism

0.7

typical for HRTS type
     

subtotal

63.6

  

margin

9

  
     

total

72.6

  

not included: purge harness, radiator/thermal shielding, etc.

 

 

 

EIS mass estimate (Cassegrain)

    
     

item

mass (kg)

basis for estimate

electronics box

11

based on single string compact PCI box
   

available from Lockheed Martin
   

9 kg for the populated box and cards
   

2 kg for thermal/mechanical hardware
   

CPU is the RAD-6000, 32bit 30MHz
   

RISC processor
   

Box has slots for 8 3U format cards

structure

15

fully composite structure
   

6kg for skin
   

9 kg for stiffening elements

door mechanism

1.4

scaled from LASCO

camera

1.5

typical for present day cameras

primary mirror

3.5

21cm dia x 4 cm thick
   

Zerodur 2.5g/cm^3

mirror mount

0.5

hub mount

spider

1

typical for HRTS

secondary mirror

0.2

7diax2cm thick

scan/focus mech.

1.6

typical for compound pzt/motor mechanism

grating

0.9

11x12x3cm

grating mount

0.3

typical

grating focus mech.

0.8

typical for HRTS

shutter

0.3

typical for direct drive mech.

slit/slot mechanism

0.5

typical for wheel mechanism

filter frames

0.2

reasonable Al structure

evacuated cavity

2.5

same as TRENDY version

MLI

2

15 reflector blankets

sunshield

0.5

perhaps not required for Cassegrain

cables

4

typical for LASCO cabling

mounting legs

2

typical for LASCO type legs

launch lock

1

typical for LASCO type launch lock
     

subtotal

50.7

  

margin

9

  
     

total

59.7

  

 

 

 

 

 

 

 

 

 

 

 

 

scaled version of TRENDY

      

scale factor =

0.82

    

item

mass (kg)

scale factor

scaled mass

electronics box

11

1

11
       
       
       
       
       
       

structure

25

0.6724

16.81
       
       

door mechanism

1.4

0.82

1.148

camera

1.5

1

1.5

primary mirror

2.6

0.551368

1.433556
       
       

mirror mount

0.5

0.82

0.41

scan mechanism

2

0.6724

1.3448

grating

2.2

0.551368

1.213009
       

grating mount

0.5

0.82

0.41

grating focus mech.

0.8

0.82

0.8

shutter

0.3

1

0.3

slit/slot mechanism

0.5

1

0.5

filter frames

0.2

1

0.2

evacuated cavity

2.5

0.82

2.05
       
       
       

MLI

4

0.6724

2.6896
       

sunshield

0.9

0.6724

0.60516

cables

4

1

4

mounting legs

2

1

2

launch lock

1

1

1

slit focus mechanism

0.7

1

0.7
       

subtotal

63.6

  

50.11412

margin

9

  

9
       

total

72.6

  

59.11412