1. MDP / DHU - DR Usage vs downlinks -
Keiichi MATSUZAKI
(ISAS)
I’m Keiichi MATSUZAKI from ISAS.
Here, I briefly summarize the capability and the usage of Mission Data Processor and Data Handling Unit which controls Data Recorder.

2. Data Flow from Telescope to Ground
Software guard for total volume in certain period is possible
Buffer
12Mbps
SOT
SOT
1400kbps
(2000)
~2.4Gbits /downlink
(4Mbps)
Bit
Comp. +
Image
64Mbits
3Mbps
XRT DR
XRT
300kbps
(0)
>5Gbits
64Mbits
Next, I’ll present transfer and processing of observational data from telescope to the ground.
Every observational data in Solar-B goes by two instruments, MDP and DHU, before it reaches to the ground. MDP has capability of bit compression and image compression for all telescopes. DHU has Data Recorder, which will be played back at ground contacts.
Physical line from MDP to DHU is shared by three telescope by time sharing. Allocated band pass for SOT, XRT & EIS is nominally 1400kbps, 300kbps, 300kbps, respectively.
Processing speed compression block is fast enough and transfer from telescope to inside of MDP is limited by speeds of interface line or performance of telescope itself.
In order to solve possible inconsistency between two speeds, small buffers exist in MDP for each telescope.
2Mbps
EIS
EIS
300kbps
(0)
64Mbits
MDP
DHU
Earth

3. Pre-flare (mode trigger) buffer for XRT
Normal
(FIFO 16Mbit)
Ring-1
12PFI
Ring-2
18PFI
In the case of XRT, the buffer has special function in addition to the normal function.
The buffer is divided into 4 sections. One for normal purpose, and the others for ring buffers.
The data put into ring buffers are discarded in the orbit unless the flare happens.
However, contents are frozen at the timing of the flare detections and the contents can be down linked after the flare occurrence. In this way, XRT can achieve higher cadence inverse-word from the timing of the flare detection.
Ring-3
28PFI
PFI < 256x256 (for larger image # of image decrease)
Quiet
mode
Flare
mode

4. Data Recorder Simple ring buffers (size > 8.0 Gbits)
One partition for SOT, XRT & EIS (+MDP)
One partition for S/C
No priority control
Stop or full (selectable)
Simultaneous Recording & Downlink
One partition for downlink
All of the observational data obtained by Solar-B once be recorded by the data recorder and be played back at ground contact.
There are two partitions: one for observational data and the other primary for S/C.
Both partitions are simple ring buffer. At a given moment, two partitions can be recorded and one partition can be played back simultaneously.
Capacity of the DR is larger than twice of amount played back in one downlink.
The data recorder can be either stop or overwrite when it becomes full by accident.
Record
(Write Pointer)
Play back
(Read Pointe)r

5. Down link 4Mbps(X-band) 150 minutes of down-link / day
Bottle neck for total amount of data
32kbps(S-band) - For S/C
150 minutes of down-link / day
4 KSC + 12 Polar stations / day
2.4Gbits/downlink, ave. recording rate 400kbps
Downlink bandwidth from the onboard system to the ground system is 4Mbps in nominal mode, which is twice of peak bandwidth from MDP to DHU. Since the coverage of downlink is less than 10%, total amount of data which can be obtained by Solar-B is strong;y limited by number of downlinks. Assuming 75minutes downlink by 8 stations in a day, average recording rate of 200kbs after compression can be realized.

6. Example of Sharing of Telemetry (per downlink)
SOT
1400Mbits (70%) FG
1100Mbits
(55%) SP
300Mbits
(15%)
XRT
Partial
Frame
225Mbits (11.25%)
Full
75Mbits (3.75%)
EIS
Data recorder is shared by three telescopes. Allocation, or target for amount of observation, of the storage per downlink will become these values assuming the ratio of 70%, 15% and 15% for SOT, XRT and EIS, respectively. This nominal ratio can be modified in the weekly meeting.
Each telescope can further divide storage into detailed usage.
Ratio can be modified in Weekly Observation Meeting depending on campaign

7. Example 1 Constant Rate with Clean up of DR
Play back
250kbps = 8 pass/day
From this chart to the last chart, I’ll present some examples of observations which can be achieved by the Solar-B system. In these plots:
Vertical axis corresponds to the position of read & write pointer of DR in a unit of G bits.
Horizontal axis corresponds to time in minutes.
In the first example, there are two downlink stations at time zero and 200 minutes. At the end of the first contact data recorder is cleaned up. The same is the case at the end of the second contact. Between the two contacts, data rate is constant.
1Rev.
2Rev.

8. Example 2 Burst Rate with Clean up of DR
Play back
2000kbps Total 20min
In the next case, again data recorder is clean up at the ends of the first and second contacts.
But in this case observation is confined to the 20 minutes distributed between contacts.
Stop
Obs.
Stop
Obs.
Stop

9. Daily Allocation for Chief Observer
2003/2/4 10:00:00 2.5
2003/2/4 12:00:00 2.5
2003/2/4 14:00:00 2.5
2003/2/4 10:00:00 3.2
2003/2/4 12:00:00 3.2
2003/2/4 14:00:00 3.2
Downlink start time
Allocated Volume for Planning
Data recorder is shared by three telescopes. Allocation, or target for amount of observation, of the storage per downlink will become these values assuming the ratio of 70%, 15% and 15% for SOT, XRT and EIS, respectively. This nominal ratio can be modified in the weekly meeting.
Each telescope can further divide storage into detailed usage.
Limit Set by MDP for telemetry guard
Format is TBD

10. Example 3 Mixed Case, Empty out of DR
The next is mixture of the former examples.
In this case, FG and XRT are carrying out constant rate observations while SP and EIS are carrying out burst type observations.

11. Example 4 Average Rate ~ day
Margin for uncertainty
Flare event
Compression Result
2000kbps合計20分
DR size
= 8.0G bits
The last example covers movement of pointers during a period of one day.
In this example:
There are 4 contacts after the first contact.
Data recorder is cleaned up only at the end of the first and the last contacts.
In this chart: Height from pink line to the orange line corresponds to the size of DR.
In order to keep DR from filling up, blue line cannot cross the orange line.
Since the DR has size larger than twice of a downlink, we can realize nearly constant observation.
Although this plot is for all telescopes, similar plot can be made for each telescope.
In that case height from the pink line to the orange line will be substituted by allocation for each telescope. 休止 観測 休止 観測 休止