Lunar Lander Data Acquisition and Control
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This page still needs a lot of editing. It focuses mainly on the laser range finding characterists yet it include IMU and GNC units. Can someone clean this up? --Sean Casey 18:14, 17 August 2009 (EDT)
Related tasks::Tasks:Laser_Rangefinder
Contents
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DATA ACQUISITION
SYSTEM LEVEL CONSIDERATIONS. Laser Range Finder (Altimeter)
By: Dr. John L. Barrett
At the system level the requirement is to range to 50km with an accuracy of 1m using a lightweight, eyesafe device. The requirement will be met by operating at 1.06microns; we will use this wavelength for the detector.
We will impose a (single pulse) probability of detection of 0.9, and a false alarm rate below 0.02 per second. For pulse detection in white noise the required signal to noise ratio is 7.8.
The stringent range accuracy requirements do not allow the use of a simple threshold circuit to stop the range clock. Instead a constant fraction detector (CFD) will be used. This guarantees that the range counter will be stopped at the same relative point of the detected return pulse over large variations of received pulse amplitude. This circuit reduces the signal to noise by a factor of 1.4 therefore requiring an increase in S/N of that amount to maintain system performance.
The uncertainty in range is
ΔR = τR C/20.5 S/N
which, for the numbers developed below, is 0.25 m.
DETECTION AND NOISE. Laser Range Finder (Altimeter)
The EG&G C30700-0900 InGaAs avalanche photo-diode integrated with preamplifier has a noise equivalent power (NEP) of 1.72 x 10-13 W/(down)Hz. A bandwidth of 60MHz (matching the 6ns pulse) will give detector/pre-amp noise of 1.33 x 10-9 W. As will be seen this is the dominant noise source.
We assume a beam filling target of reflectivity 0.1. Under this condition the background noise will be far smaller than detector/pre-amp noise. After the transmit power requirement is determined, it will be seen that shot noise due to collected signal is also small.
RANGE PERFORMANCE CALCULATIONS
The irradiance of the target (in w/m2) by the laser is given by
E = PL·TT/A
where PL is the laser transmit power TT is the transmission of the optics (0.6) A is the irradiated area.
The fraction of the light returned per unit solid angle is Aρ/π where ρ is the target reflectivity. The amount of the scattered light collected is proportional to the solid angle subtended by the collecting optics at the target that is
Ω = πD2/4R2
where D is the collector diameter R is the range to the target.
The return flux is again attenuated by the transmission of the receiver optics. The signal power is
PS = PL ρ TR TT D2 /4R2
The values used were D = 0.1m ρ = 0.1 TR = TT = 0.6
Transmissions include a 10nm wide optical filter to reduce background noise. The expression was evaluated at maximum range, 50km.
PS = 3.6 x 10-14 PL W
giving signal power in terms of laser power. Combining this with signal to noise requirements
S/N = PS/NEP 1.4 X 7.8 = 3.6 x 10-14 PL / 1.33 x 10-9 PL = 4.06 x 105 W/pulse
For a pulse length of 6ns this requires 2.5mJ of energy. Average signal power is 25 mW at a repetition rate of 10 Hz.
If we assume a responsivity of 100 A/W the signal generates a current of IS = 1.45 x 10-6 A. This will have a noise component of
iS = (2 e IS BW)0.5 = 5.3 x 10-9 A
which corresponds to a power of 5.3 x 10-11 W, well below the detector/pre-amp noise and therefore negligible.
REQUIREMENTS. Laser Range Finder (Altimeter)
Assumptions
Reflectivity of moon surface (lunar albedo)
Source: Lunar regolith emissions
- Assumed: 10% @ 1064 nm
Descent Characteristics effect require laser characteristics ??
- Vehicle speed
- time for delta v
- burn pattern
Probability of pulse detection
- Single pulse probability of detection of 0.9
Physical aspect
Source: Ryan's preliminary budget
- weight: < 2 kg
- size: < 0.3x0.2x0.1 meters
- power draw: 10W only in Land Sequence
Operating Voltage
Source: Many space qualified Hardware under consideration work in the range of 22 to 30 VDC
- 28 VDC (bus voltage)
- Can-do bus provide 5 volts for COTS at this range
Range resolution
Source: Landing_Simulation Range is a trade of: cost/complexity vs Resolution
- Suggestion: +/- 1 meter (almost 5 m because LIDAR coverage is from 30/50 m to ground)
- Required: 10 km ground (Goal: 70 km to ground)
- @10 km
- Z resolution 10 meters,
- Y resolution +/-500 meters and
- X resolution +/-100 meters.
- @1 km
- @10 km
- Z resolution 1 meter
Update rate
Source: Lunar_Lander_Data_Acquisition_and_Control
- Assume the laser achieves a 3nanosecond pulse width, 6 nanosecond peak to peak?
- Required > 70 km:
- Update rate < 1 Hz
- Required < 50 km
- Update rate from 10 - 100 Hz
Required bandwith
- RF Bandwith 58 MHz
False alarm rate
- Required: <0.01
Wavelength of Laser
- Required: 1064 nm
Collector/Detector Aperture
- Required: 10 centimeters
Cost Constraint
- Required: < $20,000 USD
Some recomendations
On Fri, Nov 6, 2009 at 8:41 PM, eric gustafson wrote:
Guys,
I've been watching all the activity on the Lander Group page lately and its great to see that much work going on.
On the front of the Laser Rangefinder I'm supposed to be working on, I haven't done much.
I did send an email out to the gentleman from Japan, Leon, a couple of times, giving him a few ideas about what tasks I was looking into performing next, but did not hear back from him. I'm not sure if his spam blocker was at fault or what, but if you can get him to head up the effort that would probably be the best course of action.
My specialty is optomechanical engineering and design. So, if it is decided that we want to build a customer laser rangefinder or want to modify an existing one, then I can help with that design and fabrication effort. As for the systems engineering that would precede that effort, I would struggle with being efficient on most aspects of those tasks.
My colleague, John Barrett, who is in retirement has indicated he is no longer interested in helping me out much beyond what he has already done for us. So, unfortunately I don't have him to do all of the Systems Engineering work for me anymore.
So, if you guys could try to get Leon or someone to head the Laser Rangefinder effort, I would be willing to help with Mechanical Design, Thermal, Vibrational, Optomechanics of the device, but cannot really offer too much expertise beyond that, basically due to time constraints that I've been struggling with, and the fact that I'm not a laser physicist or a systems engineer. I would be highly inefficient at these tasks on my own.
-Regrets,
On Sat, Nov 7, 2009 at 3:11 AM, eric gustafson wrote:
Gentlemen,
Two things. First off, on a parting note from Dr. John Barrett the last time I met with him, he said the following two things would significantly simplify the design of the laser rangefinder.
"Don't make it a varialbe frequency system. Make it 10 Hz. that will save on system power requirements, thereby, significantly simplifying the design. This will cut down on the size, weight, cost and power draw for the laser rangefinder."
"Only use the laser at 50km and closer, try to use some other means to determine position before you get to the 50km point." (also simplifies the design in terms of size, cost, weight, power draw).
2nd, here is a cut and paste from the email I sent Leon:
EMAIL TO LEON: I had some ideas for you, basically, this is what i've been meaning to do:
Investigate variable frequency system. Are there existing systems that can do variable rates, if not, brainstorm some possible ways we might achieve variable frequencies. This is in regards to the previous emails:
-What is the required Update Rate: (>70 km 1 Hz. From 10 to 100 Hz at low altitude <50 km (Source:Lunar Lander Data Acquisition and Control)
Look at the list of COTS Laser Altimeters and see if there is anything suitable to meet the requirements as listed here....
Re-investigate existing Laser Altimeters to see if there is something existing we an already use, or if there is something we can base our design from, for instance an Apollo mission Laser Altimeter.
On Sun, Nov 8, 2009 at 10:54 PM, joshua tristancho wrote:
Hi Eric,
The Laser Rangefinder is a critical part in the Lunar Lander design and operation. Camera/Vision can be used to know the Lander position in far field but when near it is mandatory use this device. In addition of that, I believe we can improve very good performances and save costs if we continue with this effort in the Team FREDNET made Laser Rangefinder. As per John Barrett proposals, I can ask Jeyram and Simon K. in order to redefine the landing procedure/Path for 50 km and closer instead of 70 km. About 10 Hz, we can try to adapt to this constrain; I will take into account in the next review for the System Requirement Document and include these emails in the wiki Lunar Lander study as well. We need a very light (<1kg), reliable and space qualified Laser Rangefinder and I don't know if the market can provide all of this in a product.
As per brainstorm, If the lunar rover uses a radar, we can try to joint both devices as one. We can put the Laser Rangefinder in the lunar rover but also used during the landing phase. It is a Crazy idea.
Joshua
On Fri, Nov 27, 2009 at 8:57 PM, Jose Luis Blanco wrote:
About laser range finders:
I've had a very good experience with those by SICK. They have "directional" 1D range finders and also 2D scanners, but I think for this 1D is enough. Some models can measure up to hundreds of meters and they are quite robust to e.g. solar IR light. The problem is that most models are inexplicably pricey, heavy and power consuming.
HOKUYO manufactures cheaper, lighter and smaller models, but from by experience they are by far very sensitive to sun IR interferences.
Jose-Luis Blanco-Clarac
Hardware Under Consideration
Proposals for Altimeter
- Newcon 100 km laser range finder
- optoNCDT ILR 1191-300 300 m
- Newcon LRB25000 25 km laser range finder
- Riegl FG2L-R1 10 km Laser range finder
- Jenoptik ELEM-DP 10 km Laser Rangefinder
Background
- Laser Rangefinding (Moved)
Laser Rangefinder Summary
| P/N | Company | Range on Terra | Power (W) | Size (mm) | VDC (V) | Weight | Space Readiness |
|---|---|---|---|---|---|---|---|
| LRB25000 | Newcon Optik | 25 km | ?? | 200x200x90 | 12 | 1.45 kg | 3/10 |
| FG2L-R1 | Riegl | 10 km | 5 | 185x120x60 | 10 to 14 | 1.45 kg | 3/10 |
| ELEM-DP | Jenoptik | 40 km | ?? | 223x60x124 | 24 | 1.6 kg | 3/10 |
| LRM MOD 2/2 CI | Newcon Optik | 2.5 km | ?? | 92x86x48 | 9 | 170 g | 2/10 |
| ILR 1191-300 | optoNCDT | 300 m | 11.5 | 136x57x104 | 10 to 30 | 800 g | 5/10 |
| FREDNET Custom1 | Team FREDNET | >50 km | 10 | 150x100x100 | 28 | 1.5 kg | 10/10 |
| FREDNET Custom2 | Team FREDNET | >50 km | 15 | 200x100x100 | 28 | 1.8 kg | 10/10 |
| LD90-3 GF | Riegl | 500 m | 5 | 200x130x76 | 28 | 2.5 kg | 2/10 |
| RS100 | Opti-Logic | 100 m | 1.8 | 32x78x84 | 7 to 9 | 227 grams | 5/10 |
| Newcon Optik LRB 25,000 25 km Laser Rangefinder 1540mm | 
|
|---|---|
| Power | DC 12V Ni Cad battery (built-in) |
| Size | 200 x 200 x 90 mm |
| Weight | 1.9 kg |
| Temperature range | -20 to 60 ºC |
| Cost | US$17,999.00 |
| Riegl FG2L-R1 10 km Laser Rangefinder | 
|
|---|---|
| Power | DC 10-14V, 400 mA Alcaline-Manganese/NiMH 6xAA batteries |
| Size | 185 x 120 x 60 mm |
| Weight | 1.45 kg |
| Temperature range | -10 to 50 ºC |
| Cost | US$ <18,000.00 |
| Jenoptik ELEM-DP 10k 50 to 40,000 m Laser Rangefinder CAN-BUS | 
|
|---|---|
| Power | DC 24V, 8A max. Ni Cad battery (built-in) |
| Size | 223 x 60 x 124 mm |
| Weight | 1.6 kg |
| Temperature range | -40 to 70 ºC |
| Cost | US$?? |
http://www.jenoptik-los.com/data/downloads/677/ELEM-DP_10k_en.pdf
| Opti-Logic RS100 100m 3.6 to 91.5 m Laser Rangefinder Used in prototype Mark-II ASCII Protocol: RS232 - 8, N, 1 Baud Rate:19200 Accuracy: +/- 1m on 1x1m2 50% reflectivity | 
|
|---|---|
| Power | 7-9VDC conditioned required Current draw @ full power (~ 1.8W) |
| Size | 32 x 78 x 84 mm |
| Weight | 227 grams |
| Temperature range | -20 to 55 ºC |
| Cost | 470 US$ |
http://www.opticsplanet.net/printable-opti-logic-range-finder-rs100.html
Proposals for IMU
- Honeywell MIMU
- Memsense 65
IMUs Summary
| P/N | Company | Range on Terra | Power (W) | Size (mm) | VDC (V) | Weight | Space Readiness |
|---|---|---|---|---|---|---|---|
| MIMU | Honeywell | ? | ? | ? | ? | ? kg | 10/10 |
| 65 | Memsense | ? | ? | ? | ? | ? kg | ?/10 |
edit Inertial Measurement Unit list
| Honeywell MIMU Main 25 g | 
|
|---|---|
| Power | 28 to 100 VDC 32 Watts |
| Size | Diam. 233 x 169 mm |
| Weight | 4.77 kg |
| Temperature range | -30 to 65 ºC |
| Cost | US$??? |
http://www51.honeywell.com/aero/common/documents/myaerospacecatalog-documents/MIMU.pdf
| Memsense 65 up to 10 g, 1200 º/s I2C and RS422 | 
|
|---|---|
| Power | 5.4 to 9.0 VDC 120 or 140 mA |
| Size | 46.6 x 22.9 x 13.9 mm |
| Weight | 0.02 kg |
| Temperature range | 0 to 70 ºC |
| Cost | US$??? |
http://www.memsense.com/images/downloads/65/Datasheet-v2.11.pdf
Proposals for Star Tracker
- Aeroastro Miniature Start Tracker
- Terma Star Trackers 5
Design
A star tracker is a photometric application, so physical pixel size, sensor frequency response, optical aperture and focal length determine the relation between star magnitude and image size (pixel count). Would be useful to have this sorted in a nice way.
Computation
A hierarchical triangulated mesh (HTM) can be used to categorize the celestial sphere. See GSC HTM.
Within an HTM segment, a number of alternative algorithms for identifying the orientation and location of an image are in use around the world. We could review some, here.
Catalogs
The GSC II is a primary, a product of the Hipparcos mission.
NOMAD is employed in some contexts.
Software
The GSC collection is one place to start.
See Astrometry.net: create correct, standards-compliant astrometric meta-data for any astronomical image.
Sim / Ground
The ESA "Hipparcos" Java is related.
Products
| P/N | Company | Range on Terra | Power (W) | Size (mm) | VDC (V) | Weight | Space Readiness |
|---|---|---|---|---|---|---|---|
| Miniature | Aeroastro | ? | ? | ? | ? | ? kg | ?/10 |
| Star Trackers5 | Terma | ? | ? | ? | ? | ? kg | ?/10 |
| Aeroastro MINIATURE STAR TRACKER Main Spec | 
|
|---|---|
| Power | DC 12V Ni Cad battery (built-in) |
| Size | 200 x 200 x 90 mm |
| Weight | 1.9 kg |
| Temperature range | -20 to 60 ºC |
| Cost | US$17,999.00 TBR |
http://www.aeroastro.com/datasheets/Miniature%20Star%20Tracker.pdf
| Terma STAR TRACKERs5 Main Spec | 
|
|---|---|
| Power | DC 12V Ni Cad battery (built-in) |
| Size | 200 x 200 x 90 mm |
| Weight | 1.9 kg |
| Temperature range | -20 to 60 ºC |
| Cost | US$17,999.00 TBR |
http://www.terma.com/multimedia/Star_Trackers5.pdf
Saved searches
Proposal for attitude control
- PID controller
PID basics
PID wikipwdia
In the following you can see any convinations for PID controllers and the Matlab(R) source (Matlab is not Open Source).
P. Proportional Controller
PD. Proportional Derivative Controller
PI. Proportional Integral Controller
PID. Proportional Integral Derivative Controller
Questions
Questions to be remove from here soon
see talk page.
