Findings & Concerns

Meeting of June 29, 1999
Sounding Rocket Working Group
National Aeronautics and Space Administration



1.  NSROC Beginnings

The Sounding Rocket Working Group (SRWG) is encouraged that the implementation of the NASA Sounding Rocket Operations Contract (NSROC) has gotten off to a good start.  We are particularly pleased that NSROC management has retained the core group of first-class contractors at Wallops.  The many ideas presented at the meeting by NSROC managers, including ideas concerning facilitating software and hardware sharing between groups, were well-received.  In general, NSROC’s apparent openness to input and communication was particularly heartening to the user community.


2.  Next Generation ACS Specifications/Fine-Pointing

The most commonly-used fine-pointing ACS configuration on NASA sounding rocket astronomy payloads is the Aerojet Mark VI platform with a Ball star tracker, which yields a typical pointing stability of 5'' rms.  Recent advances in ground-based and orbiting, space-based spatial resolving power are routinely less than 1''.  The SRWG believes the next generation sounding rocket fine-pointing capability should be better than 1'' in order to remain competitive with the rest of the field.  Towards this end, a new digital Mark VI will be flown on Cruddace/36.162 DG and we look forward to reviewing the performance of this new system.  However, it is equally important to improve the pointing accuracy of the ACS star tracker.  The current Ball star tracker has a number of limitations, namely a 4th magnitude brightness limit, the ability to track only 1 target within a 4 degree field of view, and a noise equivalent angle of 3'' at Oth magnitude that grows to 9'' at 3th magnitude.  In addition, these trackers are no longer manufactured and the stock is dwindling.

A new star tracker is desired that can track multiple faint targets within the same field of view and be functionally compatible with the digital Mark VI.  Star trackers tend to be expensive, i.e., in the $100K -- $1M range.  Given the limited resources of the suborbital program, we believe supporting experimenter-led development efforts is a more cost-effective approach.  Towards this end Aerojet has developed a standardize interface that will accept user-provided error signals, which will be tested on Clarke/36.174 UL.  They will provide ACS with “quad-cell” error signals while tracking Jupiter, which is very bright (-2.5 magnitude).  A more sophisticated effort is being lead by Nordsieck at UW-Madison who has made considerable progress in developing and testing a direct replacement to the Ball star tracker with the aforementioned capability.  Last April (1999) on Nordsieck/36.172 UG, this group flew their CCD star tracker (ST5000) alongside the Ball tracker.  They successfully tracked the guide stars acquired on route to the science target and provided low bandwidth imaging and pointing monitoring of the gyro tracking on the science field.  UW-Madison has recently been awarded an Explorer Technology Grant to further develop their low cost tracker; their reproduction cost target is $50K.  (Further details may be found at the following web site:  We note the successful development of such a low cost and highly capable tracker may represent a significant marketing opportunity for NSROC. 

We recommend that Wallops and NSROC pursue these innovative ideas for improving fine-pointing ACS systems and, in particular, that the University of Wisconsin-Madison tracker be made available to the wider sounding rocket community, if indeed that system proves successful and cost-effective.


3.  Next Generation ACS Systems/Coarse-Pointing

The SRWG finds much need for improvement in the utilization of coarse-pointing ACS systems on sounding rockets.  An informal poll of sounding rocket users indicates that there is a range of operation problems regarding the use of coarse-pointing ACS systems including inertial pointing inaccuracy and firing at inopportune times, including times inside the dead band.  These types of ACS problems can lead to serious compromise of the science objectives because instruments do not end up oriented as desired or the firing operations disturb the scientific measurements.  The reasons for the occurrence of these problems is varied, but appear to arise from insufficient system level (payload and ACS) testing coupled with less than ideal communication between the manufacturer (which does the ACS programming) and the payload team. 

It is recommended that these problems be mitigated by improving the ACS system-level design, by testing, and by ensuring that all key parties, including the payload development team, scientific team, and ACS manufacturer team, clearly communicate with one another.  The ACS operations and timeline should be fully understood and achievable within the operational constraints of the payload and ACS systems.  It may be advisable to put in place a separate review meeting (which could be conducted via telephone) among these key parties to ensure that all agree on the approach and implementation for the ACS system on a given rocket. 


4.  Next Generation “Coarse” Attitude Systems

Another area of long-standing concern of the scientific user community and the SRWG in particular involves “coarse” (i.e., ~ 1 degree knowledge) attitude solutions.  These solutions are frequently supplied to the science teams only to be subsequently determined to be inaccurate.  Consequently, a great deal of effort is expended by the science team to both verify and develop acceptable solutions which should, in principle, be an accurate data product when delivered to the science team.  It is not clear exactly where the problem lies, but the technical specifications of the attitude systems indicate that accurate solutions should be routinely obtainable.  One area where inaccuracy may creep in is through the use (or lack thereof) of accurate calibration data for the specific attitude system. 

The standard payload system used to provide coarse attitude knowledge for most space physics payloads in the MIDAS gyro platform.  These gyros utilize a design that is over 25 years old.  Although a dependable "workhorse" of many NASA sounding rocket payloads over the years, these gyros have recently been shown to be noisy and to include unacceptable drift.  Based on the presentation at the last meeting, we understand that a new procurement of attitude sensors is being carried out by NSROC and we urge that ease of data analysis and interpretation be taken into account, in addition to standard evaluation factors such as in-flight performance (accuracy, noise, drift), size, power, telemetry, cost, etc.

The SRWG believes that Wallops should clearly specify with whom the responsibility lies to determine if a given attitude solution is accurate and acceptable (e.g.., Wallops? NSROC? Attitude manufacturer?  Users?)  We urge Wallops to enact a process with which to verify the attitude solutions post flight before delivery to the science teams.


5.  User's Manual

In the past, Wallops has provided a “User’s Manual” for P.I.s which explained many of the basics of the program and helped new researchers get started.  The User's Manual should provide a common location for information for Sounding Rocket PI's and engineers, including vehicle performance, NASA facilities, and documentation requirements.  In addition to T/M and electrical requirements, it would be useful to include information about the ACS system data, such as details about how to interpret the MIDAS gyro data.

The current manual is out of date, and we encourage Wallops to update this information, particularly now that NSROC has been enacted.  To this end, the SRWG would be more than happy to contribute to this endeavor, including reading of drafts and providing feedback.


6.  Reviews/Independent Oversight

Several recent mission failures and near-failures have been caused by planning errors that should have been caught in reviews, such as mis-matched time-lines.  This seems to point to a need to make the reviews more technically rigorous.  This includes both Design Reviews and Mission Readiness Reviews.  Impartial overseers with mission heritage should be present at the reviews, and required to ask hard questions.  This appears to be especially necessary at the present time because of the large turnover in engineering personnel.


7.  New Systems/Purchases  --  SRWG input

The SRWG notes that several important procurement decisions will be made by NSROC over the next year, which could have significant impact on the scientific capabilities of the payloads and hence the sounding rocket users.  These include decisions on a new rocket motor purchase, new gyro or other attitude platforms, standardization of TM stacks, and development of new ACS systems.  The SRWG would like to be involved in the specifications for these and similar items that will impact the system, reliability, and scientific capabilities of the payloads for future flights.  For example, we would like an opportunity to comment on the draft RFP concerning the requirements and specifications for the other systems mentioned above.  This requires a closer working relationship between the NSROC contractor and the SRWG than has existed to date.  A simple mechanism, which should not adversely impact the NSROC procurement process, might be to alert the SRWG to draft RFP information, particularly in cases where such a draft RFP is made public to potential bidders for comment prior to release.


8.  Availability of TM Simulators

The Sounding Rocket Working Group strongly believes that experimenters, contractors, and NASA would all benefit from the development of a portable, PC-based telemetry interface emulator.  As envisioned by the panel, these could take the form of plug-in PC boards or stand-alone modules built around the same hardware that NASA uses in their current TM systems.  The emulator systems would be programmable in the same way that the flight TM systems are now programmed, and would be capable of producing the same synchronization and ENABLE signals as the flight systems (e.g., word clock, bit clock, frame synch, parallel word enable pulses, and serial handshaking signals).

Several experimenter groups already have developed or purchased key components of such systems, but no standard is in place and none of these systems uses all the same parts as the NASA TM systems.

There is a substantial cost savings to be realized by providing such standardized development systems to experimenters prior to integration.  First, such systems would allow experimenter teams to solve telemetry interface problems at home on the bench instead of during the Wallops integration process.  Telemetry interface issues are among the most common and time-consuming integration problems.  Availability of standard emulators would optimize use of the TM groundstations, allowing more payloads to be processed in less time.  Secondly, it is likely that availability of emulators would lead to a reduction in travel costs by the experimenter teams, and fewer overall problems during integration.

The Working Group recommends that a dozen such systems be created at Wallops.  These could then be loaned to experimenter teams involved in active payload development activities.  (The simulators could be returned at the Mission Readiness Reviews, for example.)

Implementation of a plan such as the one described here would likely result in shorter integrations, fewer scheduling problems with TM groundstations, and improved utilization of contractor resources.  Despite these many advantages, we note that the SRWG has made this recommendation in the past and in each instance, it has received strong support from Wallops management.  We thus urge that concrete steps be taken to make this idea a reality.


9.  SPARCS Command Uplink System and ACS Optics Support -- Uplink Command and Optical Simulators at WSMR 

We applaud NSROC for maintaining the existing corporate memory in the sounding rocket support personnel both at WFF and the White Sands Missile Range (WSMR).  We note however two areas that require immediate attention at White Sands:  programming support for the command uplink system (CUS) and ACS optics support.

A recent effort to make the CUS a “turn-key” system has been successful for the most part. However, we have lost the capability for making fiducial markings (overlays) and selectable cursors for reference and target identification.  During one of the last flights (Feldman/36.136UG) the reference cursor was so large that it obscured the slit of the spectrograph frustrating the ability to make accurate point adjustments.  In addition, the cursor colors were red and green while the Feldman CUS operator is red-green color blind.  The capability to generate programmable overlays for accurately positioning field stars in the target region was not available and compromised operator tracking knowledge and data quality.  We recommend that a programming effort be established to enable the “turn-key” CUS to provide widget driven selection options for these features.

It has also come to our attention that the star simulators (collimators) at WSMR and WFF are in need of maintenance.  Current NSROC personnel either are too busy or lack the optical expertise to maintain these systems.  In particular the collimator at WSMR is badly out of focus and the elevating mechanism is broken.  Problems have also been encountered at both at WFF and WSMR with the ACS “cradle,” a table upon which the payload is placed to simulate ACS pointing maneuvers and allow for CUS practice during integration.  We recommend additional resources be expended to properly maintain these critical testing systems.

NASA Sounding Rocket Working Group

Dr. Robert F. Pfaff, Jr. (Chair)
NASA/Goddard Space Flight Center

Prof. David Burrows
Pennsylvania State University

Dr. Joseph Davila
NASA/Goddard Space Flight Center

Dr. Greg Delory
University of California at Berkeley

Prof. Greg Earle
University of Texas at Dallas

Dr. Mark Hurwitz
University of California, Berkeley

Prof. Craig Kletzing
University of Iowa

Dr. Kristina Lynch
of New Hampshire

Dr. Stephan McCandliss
Johns Hopkins University

Dr. David Slater
Southwest Research Institute

Dr. James Ulwick
Utah State University