Project: QB50
Project: QB50
MULLARD SPACE SCIENCE LABORATORY
UNIVERSITY COLLEGE LONDON
Author: D Kataria
TITLE: QB50 Science Unit Interface Control Document
Document Number MSSL-QB50-ID-12001 Issue 1 1st March 2012
MSSL
Dhiren Kataria
Alan Smith
Craig Leff
Mark Hailey
Rahil Chaudery
Hubert Hu
Berend Winter
Peter Coker
Alan Spencer
X
X
X
X
X
X
X
X
X
VKI
Jean Muylaert
Ruedeger Reinhard
Cem Ozan Asma
Daniel Faber
X
X
X
X
ISIS
Jeroen Rotteveel
Cesar Bernal
Joost Elstak
X
X
X
Authors:
D. Kataria
Date:
01/03/2012
Manager/Project Office
C. Leff
Date:
01/03/2012
PA:
A. Spencer
Date:
01/03/2012
Page 1 of 11
Title: QB50 Science Unit Interface Control Document
Doc. No. MSSL-QB50-ID-12001 Issue 1
CHANGE RECORD
Issue
Date
Sections
changed
Issue 1
01/03/2012
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Comments
First issue
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Title: QB50 Science Unit Interface Control Document
Doc. No. MSSL-QB50-ID-12001 Issue 1
CONTENTS
1 Introduction ............................................................................................................ 4 2 Normative and Informative documents ............................................................... 4 2.1 Normative Documents ................................................................................... 4 2.2 Informative Documents .................................................................................. 4 3 Abbreviations ......................................................................................................... 5 4 Electrical Interfaces ............................................................................................... 6 4.1 Science Unit Connector Definition................................................................ 6 4.2 Grounding ....................................................................................................... 6 4.3 EMC requirements .......................................................................................... 7 4.4 Power Budget ................................................................................................. 7 5 Command and control interface ........................................................................... 7 5.1 Data Handling and Control ............................................................................ 7 5.2 Telemetry and Telecommands ...................................................................... 7 5.2.1 Telemetry ...................................................................................................... 7 5.2.2 Telecommands ............................................................................................. 8 5.3 RDY Flag ......................................................................................................... 8 5.4 Example Sequence Table .............................................................................. 8 6 Mechanical interface ............................................................................................. 8 6.1 Accommodation and Field of View ............................................................... 8 6.2 Interface control drawing ............................................................................... 8 6.3 Surface finish .................................................................................................. 9 6.4 Mass ................................................................................................................ 9 7 Attitude Control ..................................................................................................... 9 8 Cleanliness and Contamination ........................................................................... 9 9 Operating Conditions ............................................................................................ 9 10 Handling .............................................................................................................. 9 11 Thermal ............................................................................................................... 9 12 Appendix 1 ........................................................................................................ 11 Page 3 of 11
Title: QB50 Science Unit Interface Control Document
Doc. No. MSSL-QB50-ID-12001 Issue 1
1
Introduction
This document controls the required interfaces between a QB50 CubeSat and a QB50
Science Unit.
Science Unit: As described in the call for proposals, the menu of sensors selected for
the science units is:






Ion Mass Spectrometer (IMS)
Neutral Mass Spectrometer (NMS)
Flux-Φ-Probe Experiment (FIPEX)
Multi-Needle Langmuir Probe (MNLP)
Corner Cube Laser Retroreflectors (CCR)
Thermistors/thermocouples/RTD (TH)
A Science Unit will comprise a subset of the above list. The design objective for the
Science Unit is to remain within a 600 mW power budget (duty-cycled, orbit averaged),
600 g mass budget and half a CubeSat unit volume budget (excluding forward
protuberance). 20% design margin is being held within these budgets. As the final
configuration of the Science Unit to be provided to each of the CubeSat teams will only
be made known after selection, representative mechanical and electrical interfaces with
an overall resource envelope of the design objective are provided here.
The location and interface of Thermistors within the body of the CubeSat will be
included in a later version of this document.
The location and interface of the Corner Cubes, if selected, will be included in a later
version of this document.
2
2.1
Normative and Informative documents
Normative Documents
ND1: UM-3: CubeSat Kit User manual Rev D2 issued 17 Sep 2003.
2.2
Informative Documents
ID1: Call for CubeSat Proposals for QB50 issued 15 Feb 2012
ID2: QB50 SSWG Final Report to be issued 1 Mar 2012
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Title: QB50 Science Unit Interface Control Document
Doc. No. MSSL-QB50-ID-12001 Issue 1
3
Abbreviations
ADC
Analogue to Digital Converter
CEM
Channel Electron Multiplier
DAC
Digital to Analogue Converter
EGSE
Electronic Ground Support Equipment
EMC
Electromagnetic Compatibility
EMI
Electromagnetic Interference
ESD
Electro-Static Discharge
FMMU
Flash Mass Memory Unit
FPGA
Field Programmable Gate Array
HSDR
High Speed Data Recorder
HV
High Voltage
I/F
Interface
IMS
Ion Mass Spectrometer
kbps
kilo bits per second
LEO
Low Earth Orbit
LV
Low Voltage
LVDS
Low Voltage Differential Signalling
MSSL
Mullard Space Science Laboratory
NMS
Neutral Mass Spectrometer
PCB
Printed Circuit Board
PWM
Pulse Width Modulator
S/C
Spacecraft
SEE
Single Event Effects
SMD
Surface Mount Device
SPI
Serial Peripheral Interface
TBC
To be confirmed
TBD
To be decided
TBI
To be included
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Title: QB50 Science Unit Interface Control Document
Doc. No. MSSL-QB50-ID-12001 Issue 1
4
Electrical Interfaces
There will be a single electrical connector between a Science Unit and a CubeSat. The
Science Unit shall provide an MDM15-male connector for the CUBESAT side harness
to attach to. The CubeSat shall provide power, clock, the I2C interface bus and a single
bit port (RDY) signal as shown below.
GND
GND
SCN
SCN
SCL
SCN
SDA
SYS_CLK
RDY
+3V3
+5V
SCN
+3V3
Science Unit Connector Definition
+5V
4.1
Figure 4-1 Connector Pin-Out Diagram
Pin
Signal Name
Comment
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
+5
+3V3
SCN
SYS_CLK
SDA
SCN
GND
+5
+3V3
RDY
SCN
SCL
SCN
GND
Power for +5V logic
Power for +3V3 logic
Screen for SYS_CLK
7.4 MHZ (TBC) S/C system clock
Not used
I2C serial data signal
Screen for SDA
System GROUND
Power for +5V logic
Power for +3V3 logic
This may connect to any available INPUT port pin on the S/C processor.
Screen for RDY
I2C serial clock signal (100 kHz)
Screen for SCL
System GROUND
Table 4-1 Instrument Connector Pin Assignment
The +5, +3V3 and the GND connections are duplicated to provide redundancy in the
harness.
4.2
Grounding
The Science Unit electronics shall be electrically grounded to the CubeSat structure via
GND. The Science Unit Chassis is electrically connected to the CubeSat structure at its
points of attachment. The electrical resistance shall be <50 mΩ.
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Title: QB50 Science Unit Interface Control Document
Doc. No. MSSL-QB50-ID-12001 Issue 1
4.3
EMC requirements
TBI
4.4
Power Budget
The power budget is shown in Table 4-2. These numbers are preliminary TBC and
include the 20% design margin.
Mode
Power at +5V (mW)
Power at +3.3V (mW)
Orbit average
Peak
Orbit average
Peak
Standby
3
279
1
100
Science Mode
499
640
77
100
Table 4-2 Power Budget
5
Command and control interface
5.1
Data Handling and Control
The I2C interface shall be used to control the instrument from the CubeSat.
The I/F shall nominally operate at 100 kHz clock speed.
The Science Unit is treated as a device on the I2C bus. It shall have a fixed address,
set within the Science Unit.
A buffer (size TBD) shall be provided in the Science Unit to store the science data &
associated parameters.
Data shall be transmitted from the Science Unit to the CubeSat computer over the I2C
interface on command from the CubeSat computer.
5.2
5.2.1
Telemetry and Telecommands
Telemetry
The following telemetry packets shall be issued by the Science Unit to the CubeSat:Telemetry Packet
Science Packet
House-Keeping Packet
Engineering Packets
Table 5-1 Telemetry
The packet formats shall follow the I2C protocol and will be provided in a subsequent
release of the ICD.
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Title: QB50 Science Unit Interface Control Document
Doc. No. MSSL-QB50-ID-12001 Issue 1
Telecommands
5.2.2
Telecommands will be issued by the CubeSat to the Science Unit according to the
science operations plan being executed. Command sequences from ground shall be
time-tagged. The Science Unit will execute commands immediately upon receipt.
5.3
RDY Flag
The Science Unit shall provide a RDY level sensitive flag signal to indicate when the
SCIENCE DATA are available.
The CubeSat computer shall monitor the RDY bit to determine when to perform a
Science Packet read operation. The packets must be time-stamped by the CubeSat
within 1s of the packet generation.
5.4
Example Sequence Table
Below is given a pseudo sequence example of how the Science Unit would be run.
There may be several (TBD) sequences uploaded and stored in CubeSat memory,
which would be run at predefined times (i.e. time-tagged).
Command
Time
Comment
SU_ON
t0
Turn ON power to Science Unit; Unit will go to Standby
RUN_SCIENCE
t1
Science Unit operational mode.
STDBY
t2
Go to Standby mode.
SU_OFF
t3
Turn OFF power to Science Unit
Table 5-2 Example Sequence Table
6
6.1
Mechanical interface
Accommodation and Field of View
The Science Unit will be accommodated at one end of the CubeSat, on a 10 x 10 face.
The vector normal to this face shall be in the spacecraft ram velocity direction. This face
shall not be available for Solar cells, any other sensor or subsystem and nothing must
project forward of this face.
6.2
Interface control drawing
The mechanical interface drawing is provided in Appendix 1. The Science Unit is
designed to interface to commercially available CubeSat structures either through an
adapter or through appropriate relocation of mounting holes on the structures.
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Title: QB50 Science Unit Interface Control Document
Doc. No. MSSL-QB50-ID-12001 Issue 1
6.3
Surface finish
The overall finish for the Aluminium structure of the Science Unit shall be Alocrom
1200.
6.4
Mass
The total Science Unit mass shall be < 600 grams.
7 Attitude Control
The CubeSat shall provide attitude control with a pointing accuracy of +/-10° and
pointing knowledge of +/-2° (TBC).
8
Cleanliness and Contamination
The CubeSats shall maintain an ambient pressure due to outgassing of < 5x10-6 mb.
9
Operating Conditions
The particular operating conditions will depend upon the selection of sensors for a given
Science Unit. These will be made known at the time of selection.
10 Handling
The Science Unit shall be handled in a cleanroom environment (details TBI).
ESD protection protocols shall be followed (details TBI).
11 Thermal
At least one thermal sensor will be used to monitor the temperature inside the CubeSat
enclosure. This will be in addition to the thermistors in the Science Unit which are used
for scientific measurement.
Item
Science Unit
Operational Temperature Range
Non-Operational Temperature Range
Minimum Standby temperature
-20°C to +40°C (TBC)
-30°C to 65°C (TBC)
-25°C (TBC)
Figure 11-1 Thermal operating requirements
Page 9 of 11
Title: QB50 Science Unit Interface Control Document
Doc. No. MSSL-QB50-ID-12001 Issue 1
Item
Science Unit
Thermal capacity
TBD J/K
Alpha = TBD
epsilon = TBD
TBD mm²
TBD W/m2K
TBD
Radiative properties
Contact area
I/F conductance
Thermal interface filler
Figure 11-2 Thermal properties
Page 10 of 11
Title: QB50 Science Unit Interface Control Document
Doc. No. MSSL-QB50-ID-12001 Issue 1
12 Appendix 1
Figure 12-1 QB50 Science Unit Mechanical Interface Drawing
Page 11 of 11
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