Staging Go-No-Go Redux Squared

[FredA]

I'm looking into the FMS Co-Pilot system....not the whole system, just the sensor.

I think it should work just fine.

There is sufficient BW in the sensor to support a 5 revolution per second spin rate. With a little help, it might do better.

Using the cross-coupled (subtractive) sensors, any tilt will yeild an offset signal.
Spin will turn the signal into a sin wave output.

Just detect the magnitude of the peak of the sin and compare to a threshold.
Inhibit the sustainer ignition if it's over a preset level....easy to do with a Misson Control altimeter.

So far it looks good on paper.
I'll let you know later this summer (when launch season starts) how it works.

 

[ghost]

I have 2 solutions:
1) Use a single GPS module and compare locations in the time frame of a second or so. If the latitude/longitude don't change too much, it is basically going straight up. If not, it's not straight.
2) Use 2 very high preciscion GPS modules located in the front and back of the rocket. Compare lat/long data to determine the rocket's tilt.

 

[ghost]

No, alot simpler than that.

You have two antennas about a 1/4 wavelength apart, easy to do on rocket at 430 Mhz right?

Both antennas are fed into a mixer. You electrically rotate (switch) the antennas at some FM band frequency, lets say 108 Mhz. If one antenna is farther away from the transmitter than the other (like when the rocket is vertical) you will get a phase modulated signal (because of the arrival time difference between the antennas) that an ordinary fm receiver will pick up. If the antennas are the same distance from the transmitter (like when the rocket is perpendicular to the ground there will be no phase difference and you will get a null.

In between you will get a signal level between 0 and the vertical position. This signal will tell you what the orientation is of the rocket.

So basically you are suggesting to mount two ultrasonic sensors (except with fm waves, not sound) in the rocket? What about normal ultrasonic sensors (long range)? Even if there is a cloud below, the sensors will both read the distance from the cloud (assuming the sensors are mounted on fin tips...)

 

[Silverleaf]

...scratches melon...

Surprisingly I'm following this verbatim and so far what I'm reading is excellent. A technical report could be the sum of the whole, and be very enlightening to the masses once something concrete has been determined.

Not to give you guys a huge ego boost - since this place couldn't handle all the Texas size heads here :rotflol:, but this and Scale design is why I originally joined TRF. Kudos and please keep the ideas and succulent conversation coming. As Spock would say...

Fascinating

Cheers,

R.S.

 

[jderimig]

So basically you are suggesting to mount two ultrasonic sensors (except with fm waves, not sound) in the rocket? What about normal ultrasonic sensors (long range)? Even if there is a cloud below, the sensors will both read the distance from the cloud (assuming the sensors are mounted on fin tips...)

Similar concept. I am skeptical whether you can get an ground echo from a very high flight.

 

[bobkrech]

I have 2 solutions:
1) Use a single GPS module and compare locations in the time frame of a second or so. If the latitude/longitude don't change too much, it is basically going straight up. If not, it's not straight.
2) Use 2 very high preciscion GPS modules located in the front and back of the rocket. Compare lat/long data to determine the rocket's tilt.

Won't work.

1.) The available GPS systems loose lock at 4-6 Gs.

2.) High Precision commercial GPS units need too much time to acquire data.

Bob

 

[bobkrech]

So basically you are suggesting to mount two ultrasonic sensors (except with fm waves, not sound) in the rocket? What about normal ultrasonic sensors (long range)? Even if there is a cloud below, the sensors will both read the distance from the cloud (assuming the sensors are mounted on fin tips...)

Ultrasonic sensors have a max range of ~75 ft.

Bob

 

[jderimig]

Eye safe is ~2 mw/cm2. It's not that difficult to make a 1 watt laser eye safe by increasing the area of the beam.

You really want a 50% duty cycle to maximize detection sensivity.

Bob

Thanks Bob, I did not express my original question very well. I was wondering if the pulse time was very very short, and the duty cycle was very very low (sensitivity issues granted), would the eye safe level be higher? In other words is the eye safe level based on continuous exposure or does it matter?

Its still early for me, maybe those words aren't clear either....

 

[Art Upton]

So basically you are suggesting to mount two ultrasonic sensors (except with fm waves, not sound) in the rocket? ...)

Hi Ghost,

John is not suggesting two ultrasonic sensors.

John is suggesting a 430mhz radio beacon being beamed up from the Launch pad.

Two radio antennas 1/4 wave apart (~19") are on the body of the rocket payload.

The receiver in the rocket has an antenna switcher switching the two antennas to the receiver at about 100mhz.

Using an FM broadcast receiver descriminator chip in the rocket receive you should be able to detect the differance in antenna oriantation to the ground transmitter as a phase differance.

 

[jderimig]

Hi Ghost,

John is not suggesting two ultrasonic sensors.

John is suggesting a 430mhz radio beacon being beamed up from the Launch pad.

Two radio antennas 1/4 wave apart (~19") are on the body of the rocket payload.

The receiver in the rocket has an antenna switcher switching the two antennas to the receiver at about 100mhz.

Using an FM broadcast receiver descriminator chip in the rocket receive you should be able to detect the differance in antenna oriantation to the ground transmitter as a phase differance.

Actually I reread my TDOA references. You would beam up 433Mhz (or the frequency of your choice). The antenna switching frequency would be AF (500-2000Hz) which would produce that frequency tone. The resultant modulation deviation would be proportional to the time difference of arrival of the two antennas. So you would need an FM 433Mhz receiver module. Should still be doable economically. The antenna spacing would only be about 7". May want to try helical polarization on the antennas so the antennas can be wrapped around the airfame.

Don't think the antenna switching scenario at 108Mhz would work as I originally stated.

 

[Art Upton]

...
Don't think the antenna switching scenario at 108Mhz would work as I originally stated.

Freckin' Buggers, thats what made it sound so.....

Ingenious irate:

 

[bobkrech]

Thanks Bob, I did not express my original question very well. I was wondering if the pulse time was very very short, and the duty cycle was very very low (sensitivity issues granted), would the eye safe level be higher? In other words is the eye safe level based on continuous exposure or does it matter?

Its still early for me, maybe those words aren't clear either....

John

It can take lot's of calculations to do it correctly. See the following 2 references for details.

https://www.eyesafety.4ursafety.com/laser-eye-safety.html

https://www.answers.com/topic/laser-safety

Below is a simple chart to assist in determing required OD protection. (2 mw/cm2 is highest level of irradiance of continuous lasers that does not require eye protection for visible lasers.)

https://www.eyesafety.4ursafety.com/laser-wavelength.html

Bob

 

[FROB]

...The antenna switching frequency would be AF (500-2000Hz) which would produce that frequency tone. ...May want to try helical polarization on the antennas so the antennas can be wrapped around the airfame.

I think your right, and circularly polarized antennae would be a good choice, helical or otherwize. not only because they are compact, but to help insure good reception in all attitides.

Another variant on this theme would be to use 2 RF front-ends instead of an antenna switch, and feed both directly into a phase discriminator. That will directly output a DC voltage in proportion to the phase difference.
This might be more practical if the RF beacon you are using is also part of a telemetry radio transceiver system, carrying FSK or otherwize modulated data.

I think this will also exibit a sensitivity curve similar to the accelerometers - meaning that when the line between the 2 antenna is directly parallel to the RF propagation path, you will have the lowest sensitivity to rotation. What you want is the other way 'round i think, so i would place the antenna side-by side, perhaps at the fin tips or another suitable place, depending on the separation needed. that way, when the rocket is straight up, you have no phase difference (a null) but the slightest deviation from 'vertical' will produce a very large change in phase.
Of course there is a downside to this: now you need at least 3 antenna to cover both X and Y rotation of the airframe.

This would favor a higher frequency in smaller rockets:
at 433 Mhz, 1/4 wave = 17.3cm , just under 7"
at 915 Mhz, its 8.2cm, or about 3-1/4" which could fit inside a 4" airframe.
at 2.4 GHz , it's 3.12cm, side-by side antenna could fit in a 38mm body tube.
at 5.8 GHz, youre at 1.56cm, or about 5/8" - you can guess where that fits!

I would be temped to try it a 2.4Ghz, which is worldwide ISM band that allows relatively high power transmitters. its pretty trivial to put together a high power narrow CW beacon at this frequency. something in the 1W-10W ballpark should be enough to cover just about any HPR flight.
You don't actually need an exact 1/4 wave difference, but the sensitivity will be reduced as you move away from that.

Also remember the actual feedlines to the receiver fromthe antenna have to be equal length, otherwise there will be a fixed phase bias that won't help and may cause problems.

I'm starting to really like this concept; because you're not interested in any data on the RF signal, the receiver can be extremely simple and cheap, and your transmitter beacon too. Now if you combine that with the IR horison sensors and a little intelligence (MCU), we may have a real winning and reliable solution!

 

[jderimig]

I'm starting to really like this concept; because you're not interested in any data on the RF signal, the receiver can be extremely simple and cheap, and your transmitter beacon too. Now if you combine that with the IR horison sensors and a little intelligence (MCU), we may have a real winning and reliable solution!

Then we add a little steering on the way up for a vertical stabilization system.

 

[JimJarvis50]

I'm starting to really like this concept; because you're not interested in any data on the RF signal, the receiver can be extremely simple and cheap, and your transmitter beacon too. Now if you combine that with the IR horison sensors and a little intelligence (MCU), we may have a real winning and reliable solution!

It's amazing how much I don't know about some of the concepts discussed in this tread, but for this RF approach in particular, I'm missing something simple. What happens if the rocket takes off and is travelling horizontally or at a low angle, but away from you. You're pretty much looking at the bottom of the rocket, so no phase change from tilt relative to your position. But the rocket certainly isn't going straight up???

 

[Art Upton]

..I would be temped to try it a 2.4Ghz, which is worldwide ISM band that allows relatively high power transmitters. its pretty trivial to put together a high power narrow CW beacon at this frequency. something in the 1W-10W ballpark should be enough to cover just about any HPR flight.

While that might be a good choice for many, its not for me as that is the frequency of video streaming down from the rockets transmitter. 900mhz is the frequency of the rockets data streaming down and command and control streaming up.

5.8 might not work well either as the high power L and S band on board transmitters will be flooding the front ends of the receivers.

That is why 430 might have worked for me, far enough from the L and S band to probably not get front end overload.

What about 10ghz X band?
Lets make the ground station do radar tracking as well as provide the phase shift signal, now that would be really Kewl™

No one still has picked on about if the 6DOF unit can work or not?

 

[jderimig]

It's amazing how much I don't know about some of the concepts discussed in this tread, but for this RF approach in particular, I'm missing something simple. What happens if the rocket takes off and is travelling horizontally or at a low angle, but away from you. You're pretty much looking at the bottom of the rocket, so no phase change from tilt relative to your position. But the rocket certainly isn't going straight up???

Assuming it starts vertical you may be able to detect the tilt before it goes into cruise missile mode. But you are correct, if the flight is a long graceful arc into a horizontal flight then it will fail. Got to draw the vectors and determine where it will and won't work.

Or use a very directional antenna pointing up...that is where microwave freq would be nice, can use a dish.

That is why FROB probably suggested you combine with a redundant horizon sensing system.

 

[FROB]

While that might be a good choice for many, its not for me as that is the frequency of video streaming down from the rockets transmitter. 900mhz is the frequency of the rockets data streaming down and command and control streaming up.™

Dont give up too fast on 2.4Gig. Its a really wide band (2435–2465 MHz, or 30Mhz wide). we only need to tranmit a single pure tone, so the RF bandwidth we need is less than 10Khz. That leaves 29.99Mhz for your Video tramitter. You could easily make the beacon programmable too so you pick a specific channel far away from any others in use for telemetry, video, etc. at the site, and default to one on the band edges.
[edit: corretion, ther band is really 2400–2483.5 MHz for 1 watt max use in the US, that usually means frequency hopping though]

What about 10ghz X band?
Lets make the ground station do radar tracking as well as provide the phase shift signal, now that would be really Kewl™

Kewl... fo shizzle!
but way out of my league. i dont know too many RF engineers that are comfortable in those bands yet, and i work in the field! You can probably count all of them in the country on your fingers and toes. Maybe we're lucky enough to have one in our midst, by i wont be holding my breath.
RF test gear gets stratospherically expensive for frequencies north of 6Gig, even if you know how to use them, good luck getting your hands on any gear.

 

[FROB]

Assuming it starts vertical you may be able to detect the tilt before it goes into cruise missile mode. But you are correct, if the flight is a long graceful arc into a horizontal flight then it will fail. Got to draw the vectors and determine where it will and won't work.

Or use a very directional antenna pointing up...that is where microwave freq would be nice, can use a dish.

That is why FROB probably suggested you combine with a redundant horizon sensing system.

Yes thats part of it. they both have weaknesses but in areas that dont overlap, and so complement each other well.

I think you can also try to treat the problem the same way the accelerometer based altimers do their job. If your rocket is taking a gradual ballistic trajectory, the angle to the pad will be low but non-zero, and steadily increasing. If you integrate that over time, you can probably infer your actual angle from level, and displacement horizontally, with adequate though probably not stellar accuracy.

And yes with a highly directional antenna if you adjust the beacon power in proportion to the expected staging altitude, it would mean that if youre signifcantly off-course, you loose the signal at the rocket and default to no staging allowed, even if you dont know the exact attitude, the result is safe and likely to be what's needed.

 

[Art Upton]

[edit: corretion, ther band is really 2400–2483.5 MHz for 1 watt max use in the US, that usually means frequency hopping though]


Kewl... fo shizzle!
but way out of my league. i dont know too many RF engineers that are comfortable in those bands yet, and i work in the field! You can probably count all of them in the country on your fingers and toes. Maybe we're lucky enough to have one in our midst, by i wont be holding my breath.
RF test gear gets stratospherically expensive for frequencies north of 6Gig, even if you know how to use them, good luck getting your hands on any gear.

We need to use a ham license to use anything in the US that is not FCC part 15 certified and approved. So for any of this we need ham licenses.

The 1 watt is for Spread Spectrum radios that are part 15 certified. Otherwise you can only have +3dbm on part 15 analog certified devices. So to get any range we will be using part 97 Ham bands and non part 15/90 devices.

When a 1 watt 2.4ghz transmitter is in a payload section, any other S-band receiver will be totaly overloaded in the RF front end, even 30mhz away.

To test take a SpekTrum 2.4ghz R/C receiver in an R/C car, put on a 1 watt 2.4ghz video transmitter, and watch how far the range you get.

10ghz has had lots of work since the late 90's for ham comunnications. 10ghz dishes are small and you can get high power amps for little money.

It might also work for Radar at the same time?

 

[init 6]

Remote control idea sounds good Brad,

But look at this video here of this nearly straight rocket two stage flight:
https://BoosterVision.com/wmv/mtom.wmv

At 12,000 feet the human eye can't truly see if the rocket is straight or not until after the second stage is ignited and you can see the trail again.

What if you had a camera mounted on the rocket pointing downwards? Would you be able to determine if the rocket was straight before igniting?

From my own low level video you can quite clearly see the rocket tip over. Might be best if you had an abort switch. i.e. watch the video and if it hasn't staged by the time you start to see the rocket tip over, then disarm the ignitors.

This all assumes that you can get a reliable remote control at the alt you desire.

You'd also need to find some sort of remote video downlink

 

[Art Upton]

What if you had a camera mounted on the rocket pointing downwards? Would you be able to determine if the rocket was straight before igniting?

From my own low level video you can quite clearly see the rocket tip over. Might be best if you had an abort switch. i.e. watch the video and if it hasn't staged by the time you start to see the rocket tip over, then disarm the ignitors.

This all assumes that you can get a reliable remote control at the alt you desire.

You'd also need to find some sort of remote video downlink

Hi Colin, yes that all will work.

You can get reliable up and downlinks to do that; 900mhz command and control and 2.4ghz video down.

 

[FROB]

When a 1 watt 2.4ghz transmitter is in a payload section, any other S-band receiver will be totaly overloaded in the RF front end, even 30mhz away.

I sit corrected. it's probably a bad idea. But I'm not quite ready to completely concede that. Many modern cell phones transmit a watt yet also host bluetooth and worse GPS receivers that are phenominally sensitive.
It wouldnt be easy, but with some care shielding and really narrow-band front-end filters, one could probably make it work. but probably more trouble than its worth, and there's nothing to prevent 2 or more different bands from being supported with such a simple design.

10ghz has had lots of work since the late 90's for ham comunnications. 10ghz dishes are small and you can get high power amps for little money.

Got any links? i'd like to learn more on this. How little money we talking here?

 

[Art Upton]

I sit corrected. it's probably a bad idea. But I'm not quite ready to completely concede that. Many modern cell phones transmit a watt yet also host bluetooth and worse GPS receivers that are phenominally sensitive.
It wouldnt be easy, but with some care shielding and really narrow-band front-end filters, one could probably make it work. but probably more trouble than its worth, and there's nothing to prevent 2 or more different bands from being supported with such a simple design.

Got any links? i'd like to learn more on this. How little money we talking here?

Hi Frantz,

The cell phone TX/RX works at 849mhz or 1850mhz(pcs) with a full duplexer built in, the GPS at 1575mhz, and the blue tooth at 2430mhz lots of room between them. Also no second or third harmonic issues, as the third harmonic of 849 is 2547 about 100mhz above the blue tooth with is a digital SS protocol.

You could build duplexer quality band pass filters @ 2.4ghz ~ $100 each receiver adds some bulk.

The SpreadSpectrum digital signals get lots of benifits over analog in that respect, and quick turn about time.

Ever place your BlackBerry next to a conferance call phone or your computer speakers and hear the "razzp, razzp...tick,tic,tick.."

Its been a few years since I priced out 10ghz gear, I'll dig you up some ham links for 10ghz and post them.

Lots of work in 10ghz+ on the west coast it seems; mountain toping and tropo out to sea.

But now I'm letting the radio idea get me off track of the IMU idea. Now I'm thinking radar tracking and transponders instead of IMU.

Ohh wait, John said he planed to get me off IMUs in his first post

Edit: and If I get rid of the radar talk, it seems 430mhz is the easist and lowest cost for Johns idea for me. Others not using 2.4ghz video links might find 2.4ghz suitable at the same costs also.

Here is a source for a nice 60cm 10ghz dish and feed assy, about $158.
They seem to have taken over the antenna selections from DownEast Microwave:
https://www.directivesystems.com/

And DownEast's link as the old Ham's standby for Microwave Gear:
https://www.downeastmicrowave.com/

WOW, a $30 low power "toy" 10ghz gunplexer for experiments
https://www.edparadis.com/radar/

I still am waiting for some more talk on the 6DOF IMU solutions.

 

[overby]

10ghz has had lots of work since the late 90's for ham comunnications. 10ghz dishes are small and you can get high power amps for little money.

It might also work for Radar at the same time?

The ham gear I have wouldn't be very useful for rocketry; a DEMI transverter (2m - 10ghz) is $750 large, heavy, and runs on 12v. Then you'd need to put some control signals on top of that (I use an FT817 for the usual modes). Lots of work. Even then, a DSS dish has a 3 degree beamwidth at 10ghz which, depending on how you're using it, either makes tracking the rocket difficult (a 18db horn would work better)

As for amps: $100 for 3W and $350 for 8W. However, you don't need more than a few miliwatts for this application; you're not trying to punch through a raincloud for a several hundred kilometer QSO. You'll be line of site to the rocket.

FM using a Gunn diode will be cheaper and will probably work as well. Again, it requires some modulation scheme on top of FM but you could use something on the caliber of the single-chip APRS beacons.

As I understand it, radar requires pulse and we can't do that.

Glen, kc0iyt - 6m thru 10ghz

 

[Art Upton]

The ham gear I have wouldn't be very useful for rocketry; a DEMI transverter (2m - 10ghz) is $750 large, heavy, and runs on 12v. .....................

....As I understand it, radar requires pulse and we can't do that.

Glen, kc0iyt - 6m thru 10ghz

Thanks for the very good input Glen.
Yes, SSB transverters do not help much.
817 is a nice radio, I have the older 847

The idea at 10ghz would be to use pulses and detection on the rocket via patches.

I'm going to have to look at the pulse vs CW for ham legal.
CW is a pulse is it not?

Since your an active Upper-Microwave ham, what is your understanding on that issue?

 

[overby]

I still am waiting for some more talk on the 6DOF IMU solutions.

Hot Air, I've got; devices, data and code I don't. But this is the Internet so I'll pump out some hot air!

The 6DOF sensor combination is what "real" navigation systems use, of course that will work. Now, the details of making an inertial navigaion computer is the challenge. The sensors would have to be filtered and integrated in real-time, then used to calculate position. I can do some simple filtering, and I don't know how to do the latter, or how much CPU it will take. If that can be kept to fixed-point math and the trig functions implimented with Cordic functions, then I'll speculate that a microcontroler might have the power to do it. If not, a higher power CPU like an ARM could be used.

So there's this minor detail about some software. The Portland State Aerospace Society seems to have some of this working. I can't tell how active they are.

There may be some problems with drift on the rate gyros. I've only used the IDG-300, so the Analog Devices might be better. You can see that drift on the one set of flight data that I have ("Y" gyro that doesn't return to zero across the chart). I think a high-rate gyro for roll is required, but for pich and yaw I think the lower rate Analog Devices gyros might be sufficient.

Glen

1) the flight data I refer to was discussed on the Logomatic thread, https://www.rocketryforum.com/showthread.php?t=40132).

2) For an explaination of inertial guidance systems, try: https://www.ariel.com.au/jokes/Inertial_Guidance_Systems_Explained.html