Findings & Concerns

Combined Findings from SRWG Meeting
Meeting of November 30, 1999
Sounding Rocket Working Group
National Aeronautics and Space Administration

1.  New Rocket Motor Procurement

The SRWG was favorably impressed with the ongoing process for procurement of new rocket motors and the primary selection criteria that will be applied to the expected bids.  In particular, the SRWG agrees that the priority must be to maintain current capabilities at the lowest cost.  However, we were concerned that "added impulse" was lowest of all criteria in importance, behind even the bidder's marketing plan.  For some payloads, the available impulse is an important science driver.  Although in some cases range safety or the capabilities of the recovery system limit the apogee, these constraints may be eased through new systems such as the DS-19 Impact Dispersion Control system.  In future procurements of new rocket motors, we believe that it would be beneficial to invite input and comments from the SRWG (or a subcommittee) regarding the rocket motor selection criteria.

2.  New Recovery System

The new digital S-19 system with its extended boost phase guidance capability will further reduce the dispersion in impact point.  Combined with a higher performance motor, the sounding rocket delivery systems will be able to fly higher and land more accurately than ever before.  Recovery system development, however, has not kept apace with even the current suite of delivery systems.

For example, the ORSA recovery systems are stretched to their limit.  Flights above 300 km, now routine with the BB IX with a MK70 Terrier, are exhibiting damage to the skins and exposed ORSA hardware on rentry prior to chute deploy.  The situation will only worsen if a new motor is used with higher performance than the current Black Brant.  In addition, there are no recovery systems for the high flying BB X -- XII.  Development of recovery systems for these high flyers would provide longer "hang" times for astronomy and solar payloads as well as potentially lower costs to users who do not use recovery systems at this time (typically a space physics payload) as they could rebuild upon recovery instead of starting each time from scratch.  It would also allow, in conjunction with the new digital S-19, the use of high flying BB X -- XII flights at WSMR, which could increase science return for the typical astronomy/solar mission.  We urge Wallops and NSROC to develop new high altitude recovery systems, which can keep pace with the current suite of delivery systems and which could accommodate the potential increased performance of new motors.

3.  Rocket Trajectory by GPS and Radar

Since the early days of rocket probing of the upper atmosphere, the use of radar for the tracking of payloads has been the most reliable and accurate method to obtain the rocket’s position in space as a function of time.  However, with the rapid development of GPS for very accurate determination of position for a host of applications, it is obvious that this system represents an important improvement for sounding rockets.  NASA Wallops launched the first of numerous GPS hardware systems in 1994.  The GPS has not only provided position, velocity, and time data, but also has been used for vehicle performance analysis, for locating payloads for recovery, for data time tagging, and for mother-daughter timing, separation and interferometry enabling.  Present capabilities include uninterrupted track from launch to LOS of all standard 14” and 17” diameter WFF sounding rockets with real time differential tracking and display with <10m accuracy and post mission processing <1m accuracy.

The GPS NAVSTAR Documentation states that for a single point solution, the position will be within 100 meters in the horizontal and 156 meters in the vertical 95% of the time.  A differential solution, which is more complex and takes longer, would provide more accuracy.  We request that such solutions be made available to the experimenter, when required by the science. 

With respect to the accuracy of the GPS compared to the radar, the SRWG is interested in reviewing detailed comparisons of GPS and other solutions.  For example, we understand that NASA is using the GPS data from Mission 21.122 flown at ESRANGE, Sweden, and the Swedish radar results as a test, along with other suitable missions.  The SRWG looks forward to detailed comparisons of the rocket trajectory results for all flights that used both radar and GPS.

4.  TM Simulators

The SRWG commends NASA Wallops and NSROC contractor for initiating the development of a standard telemetery simulator for use by experimenters.  This new simulator will speed the integration process by allowing experimenters to verify their hardware interfaces to the rocket telemetry system before arriving at Wallops.  It is suggested that the development of this simulator first proceed with most common type of interface, serial transfer, and then proceed to parallel transfer.  Once functionality is obtained for these two types of data transfer, it may then be desirable to add features that would give added functionality for the user.  By proceeding in this manner, the most needed features will be ready the soonest, and 'bells and whistles' can come later.

5.  Commercialization and Priority of Machine Shop

The SRWG is alarmed that the costs of the Wallops machine shop appear to be higher than the costs of comparable machine shops outside of Wallops.  It is our understanding that Wallops would offer lower cost machine work to attract new business.  Furthermore, we believe that discounts should be available to NASA-funded scientists to encourage business, better structure operations, and save program costs.  In some cases, university overhead charges might be avoided in cases where direct payment is possible.

The SRWG is also concerned that NSROC's commercialization of the machine shop will eventually lead to priority conflicts between the commercial and sounding rocket sectors.  The SRWG believes that in these cases, sounding rockets should always retain priority. 

The SRWG was impressed by the shop tracking metrics that NSROC has instituted, and presented at the December 1999 SRWG meeting, showing the month number of jobs submitted and completed.  To better appreciate the shop time allocation, we suggest that NSROC further break down this analysis to show the monthly commercial and sounding rocket shop usage (submitted and completed) along with a measure of what fraction of total shop capacity was used by each sector. 

6.  Solar ACS Future Requirements

Solar missions require accurate pointing and low jitter.  The new digital LISS has reduced the jitter to approximately 0.3 arcsec.  Improvement of the jitter toward 0.1 arcsec is required by the next generation of solar instruments.

The primary problem with the current ACS system is the relatively poor absolute pointing.  This is especially troubling for instruments which do not have full sun field of view.  Instruments with 0.1 arcsec resolution will need 10 arc sec  (100 pixel) absolute pointing error to assure that the desired solar targets are observed.  This will likely require significant modification of the current system which relies on magnetic field measurements to determine roll angle.

The SRWG urges NSROC and Wallops to develop a plan to improve the solar jitter and ACS performance in order to enable state-of-the-art observations to be made in the future.

7.  Recommendation for Dedicated Flights for Instrument Development

The SRWG recommends that Wallops implement as standard procedure a "new technology" sounding rocket test flight at a rate of approximately one/year.  The purpose is to provide continuous availability of a test-bed for new and innovative instrumentation.  The flight could be performed from WFF and instruments would be proposed through normal NASA Research Announcements.  By dedicating one such flight per year, NASA opens the door to new technology development by allowing flight tests of developing instrument concepts.

In concert with this initiative, we urge that the sounding rocket program explore obtaining additional operating funds through the New Technology branch of NASA HQ to the fullest extent possible, as discussed at the meeting.

8.  Miniaturization

The SRWG was impressed with the new miniaturized, rugged systems for use in small sounding rocket applications that are being developed under the Hardened Subminiature Telemetry and Sensor System (HSTSS) program by the Army Research Laboratory.  Such systems include rate and attitude sensors, transmitters, and data encoders that fit within less than a cubic inch of volume and can withstand loads of up to 100,000g for projectile and munitions tracking purposes.  The HSTSS program is currently developing an S-band transmitter with an output range between 250 mW and 2W at data rates up to 10 Mbits/sec, and fits on a board about the size of a quarter.  A PCM encoder is also available in a similar form factor (see figure) which is FPGA based and includes four 8 bit A/D channels.  An integrated PCM-DAC (PCM-Data-Acquisition-Chipset) combines a transmitter delivering up to 10 Mbits/sec of NRZ-L or RNRZ-L with digital and analog data interfaces, including a 16-bit parallel and a modified 115 kbs RS-232 interface.  Micro-electromechanical sensor (MEMS) based accelerometers and angular rate sensors are also being developed for attitude determination uses.

The systems described above have potential uses in sounding rocket experiments where low volumes and high g’s represent significant design considerations.  Miniature rocket systems currently under development at NASA Wallops and in foreign space agencies may be able to leverage these new devices in order to make small payloads an effective, inexpensive tool for low-altitude ionospheric science.  In addition, these devices have useful applications in deployed micro-payload constellations from mother sounding rocket payloads, such as the free-flying-magnetometers (FFMs) on the February 1999 Enstrophy payload (UNH).  These devices represent commercial-off-the-shelf (COTS) solutions for programs that may otherwise have to resort to unique development efforts for miniaturized systems.

We recommend that Wallops and NSROC explore utilizing and supporting such miniaturized systems where feasible.

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
University of New Hampshire

Dr. Stephan McCandliss
Hopkins University

Dr. David Slater
Southwest Research Institute

Dr. James Ulwick
Utah State University