NOAA / Space Weather Prediction Center

SWPC Frequently Asked Questions

General Space Weather | Effects on Earth | Noaa Space Weather Scales | ACE Real-Time Solar Wind


ACE Real-Time Solar Wind

1. Did NOAA provide any funding for the ACE RTSW system?

Yes, NOAA provided $ 680,000 to modify the ACE satellite. We contracted with the Explorer Project, APL the spacecraft builder, and the three instrument teams. The spacecraft was modified to leave on the transmitter to continuously transmit a special subset of the data at 434 bits per second (not counting the encoding, etc.).-RZ

2. Did NOAA provide any funding for the ACE RTSW ground system put together by SWPC and how does the RTSW ground system work?

No, NOAA did not provide actual dollars. We developed the ground system under the concept of a partnership, with each partner providing some contribution to the overall system. CRL in Japan provided the ground system and all the local staff at no cost to NOAA. In return for tracking ACE RTSW data in real time-the data is sent to CRL the second it is finished being processed. RAL in England is another story. They provided the ground system but we needed to pay for someone to keep it running. The USAF stepped up to this task, as part of their contribution to the program, and send us enough money each year to fund one person at RAL. So RAL is providing a lot for very little. These two stations are 100 % dedicated to tracking ACE. During the Summer they can provide nearly 23 hours of coverage, but during the Winter they can only provide about 15 hours of coverage. NASA downloads the science data once per day over a period of nearly 3.5 hours. During the download they send us the RTSW data (this was part of the NOAA-NASA agreement). No one else can track ACE when NASA is tracking, since they switch ACE to a much higher band rate for the science data dump. We also get data, on a best effort basis from the USAF AFSCN. Currently, they try to fill in any gaps in the scheduled tracking coverage. Again, this tracking is provided free to NOAA. The USAF, through their forecast center, is a partner in this program. We continue to try and expand the coverage so we can meet our goal: 96 % coverage or better every day with no gap longer than 15 minutes. Last year the CNES in France agreed to provide some limited tracking and became a partner in the program. This year we are working with ISRO in India to provide additional tracking in the early morning UTC day during the Winter months. We are also working with UCB in the hope that their new 11 m ground station will be able to track ACE. Exactly how this will work is not yet known. SWPC now provides limited coverage during the midday hours under good conditions! This is the first direct NOAA contribution to the tracking partnership. Our contribution is the ingest, processing, and distribution of the RTSW data. This is not a small contribution. During the development of this ground system, we have provided staff time to help on numerous questions from all of the sites. Some software has been developed here and placed at remote sites to help in running the system.-RZ

3. What control do we have over the ACE RTSW data and over the ground system?

Although partly answered above, we set the requirements for the RTSW bit stream and it is a set mode on ACE and can not be changed. They do have more than one mode and could use one of them in place of the RTSW mode. The ACE Project considers the RTSW system a secondary payload, thus if anything goes wrong we are not first priority. However, we built the system on a non-interference basis. Thus, there is very little that we require of ACE, just keep it in the RTSW mode-434 bits per second downlink. NASA decides when they will do a maneuver, what orbit they will maintain, etc. So far they have always tried to consider our requirements when scheduling any change in the ACE satellite. The ground system is run by SWPC and each partner contributes to the overall success. However, we don't pay CRL to track and at any time they could stop in theory. However, every partners has a vested interest in the success of the RTSW project and they all plan on continuing. In effect we control our own destiny, short of a complete disaster such as failure of the spacecraft or of a major instrument nothing will change. They like and want the RTSW system to work. The RTSW 'payload' on ACE generates enormous publicity, which appears to be the primary driver for much of what NASA does these days.-RZ

4. Could they send ACE off after a comet or something like they did for ISEE-3?

Very unlikely. This mission was designed from day one to monitor the Sun and has a very special payload designed to do just this one thing. It is only useful in monitoring the Sun. The same was not true for ISEE-3, which had the old fashion full cross-section of instruments (keep in mind I was on the ISEE -3 science team and still remember the discussions to send the spacecraft off in search of new missions). I can not think of any mission that is suitable for ACE, except the one it is doing presently. There have been no discussions of 'other options' at the science meetings. Ron Zwickl

5. What is the average delay time from the time the data leaves ACE until it is fully processed and into the operations center?

Our goal from the beginning of the program was to have all data processed and available in operations (and the outside world) within five minutes of the time it was broadcast from ACE. At the present time most high time resolution data are available within about 3 to 4 minutes. It is fair to ask could it be done any faster and the answer is no. The current delay is not due to processing but due to buffer sizes at ground systems and the record size of the actual data. If you are looking at longer term averaged data, such as 5 minute or 1 hour data, then just add about 5 minutes to the end of the average period to get the delay.-RZ

6. What kind of problems do we have in obtaining the goal of 96 % daily coverage with no gap larger than 15 minutes?

This is the goal that is hardest to obtain. This summer we made this goal about 4 out of 5 days. In the winter we are far from achieving this goal. There are a number of reasons for 'drop outs' in the data, from antenna coverage (not to often), to a programs locking up and not sending the data, to several types of network problems. The single biggest problem is improving our overall coverage-obtaining more ground systems. Each year we have improved and expect to continue to improve until we have complete coverage. -RZ


General Space Weather | Effects on Earth | Noaa Space Weather Scales | ACE Real-Time Solar Wind