Is htv risky?

You know, after hearing a bit about how the Japanese cargo vehicle is
supposed to be docked to the station, I cannot help wondering if this is
actually safe.

I mean, it has no automatic docking, it just comes to the station, and
station keeps very close while the arm from the station grapples it and
mates it rather like the mplm to a spare port.

If anything goes out of line during the grapple, the vehicle could surely
twist, and with its mass be very hard to stop before it hit something vital.
The mplm, after all is in a rigid mount when grappled, but the htv will be
free floating albeit attitude controlled one assumes. This sort of control
if it uses thrusters rather than gyros could also cause plume damage.

I've not read any discussion about all this and wondered if anyone had
brought it up previously.

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________

On Dec 2, 4:42*am, "Brian Gaff" wrote:
You know, after hearing a bit about how the Japanese *cargo vehicle is
supposed to be docked to the station, I cannot help wondering if this is
actually safe.

I mean, it has no automatic docking, it just comes to the station, and
station keeps very close while the *arm from the station grapples it and
mates it rather like the mplm to a spare port.

If anything *goes out of line during the grapple, the vehicle could surely
twist, and with its mass be very hard to stop before it hit something vital.
The mplm, after all is *in a rigid mount when grappled, but the htv will be
free floating albeit attitude controlled one assumes. This sort of control
if it uses thrusters rather than gyros could also cause plume damage.

I've not read any discussion about all this and wondered if anyone had
brought it up previously.

All those failure modes and more can happen just as easily with
Progress, Soyuz or ATV. The HTV and future spaceraft like SpaceX's
Dragon only need to approach with the grapple range area of the SSRMS,
and hold still rather than continue to close in order to accompish a
docking. Once grappled, the spacecraft is inert and can be berthed on
a CBM port at the leisure of the station crew. So it seems to me to be
a far safer mode of docking a craft to the station, not less so. It
also confers a weight savings (no docking mechanism) and reduction in
systems complexity. Both good things, plus we retain the ability to
move station racks and other bulky cargo through the large CBM
hatches. A capability that will be lost sadly when shuttle and the
MPLMs are retired.
-Mike

wrote:

All those failure modes and more can happen just as easily with
Progress, Soyuz or ATV. The HTV and future spaceraft like SpaceX's
Dragon only need to approach with the grapple range area of the SSRMS,
and hold still rather than continue to close in order to accompish a
docking.

Does it really reduce flight software complexity ? Seems to me that you
still need precise guidance, ability to stop and station keep (more so
with HTV since it will need to station keep very close to the station.

Where would HTV berth ? And how far from its berthing point will it
need to station keep for the arm to go and grapple it ? couple of metres
? 10 metres ?

ATV/Soyuz/Progress use "targets" on the station to get Kurs to guide
their approach. Does the USA side have ay such targets to allow HTV to
guide itself to proper location an orientation to be grappled ?

At least one of the cameras recently fitted was for viewing htv, as was the
gps aerial.
I gather the berthing pport will indeed be one of the bigger ports on the
nodes which have no auto docking hardware of course.
As for distance, I don't know, how much reach has the arm if sited at the
right place?

I still get the shivers but hopefully someone has actually mitigated the
risks.

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________


"John Doe" wrote in message
...
wrote:

All those failure modes and more can happen just as easily with
Progress, Soyuz or ATV. The HTV and future spaceraft like SpaceX's
Dragon only need to approach with the grapple range area of the SSRMS,
and hold still rather than continue to close in order to accompish a
docking.

Does it really reduce flight software complexity ? Seems to me that you
still need precise guidance, ability to stop and station keep (more so
with HTV since it will need to station keep very close to the station.

Where would HTV berth ? And how far from its berthing point will it
need to station keep for the arm to go and grapple it ? couple of metres
? 10 metres ?

ATV/Soyuz/Progress use "targets" on the station to get Kurs to guide
their approach. Does the USA side have ay such targets to allow HTV to
guide itself to proper location an orientation to be grappled ?

wrote in message
...

All those failure modes and more can happen just as easily with
Progress, Soyuz or ATV. The HTV and future spaceraft like SpaceX's
Dragon only need to approach with the grapple range area of the SSRMS,
and hold still rather than continue to close in order to accompish a
docking. Once grappled, the spacecraft is inert and can be berthed on
a CBM port at the leisure of the station crew. So it seems to me to be
a far safer mode of docking a craft to the station, not less so. It
also confers a weight savings (no docking mechanism) and reduction in
systems complexity.

Also, docking with APAS is fairly violent when compared to the planned
grapple and (CBM) berthing procedure. I'm not sure about the other Russian
docking mechanisms, but I'd guess that they're fairly violent as well. You
need a certain amount of force to trip the "soft dock" latching mechanisms.

Both good things, plus we retain the ability to
move station racks and other bulky cargo through the large CBM
hatches. A capability that will be lost sadly when shuttle and the
MPLMs are retired.

Lost, but perhaps not for long. Space-X's Dragon plans to use CBM's and
should provide something like 7 to 10 cubic meters of cargo return
capability.

Jeff
--
beb - To paraphrase Stephen Colbert, reality has an anti-Ares I bias.

On Sun, 07 Dec 2008 22:00:43 -0500, John Doe wrote:

Does it really reduce flight software complexity ?

Yes, but not very much.

Seems to me that you
still need precise guidance, ability to stop and station keep (more so
with HTV since it will need to station keep very close to the station.

Where would HTV berth ?

Probably Node 1 nadir now that Node 3 won't be there (Node 3 is now
baselined for Node 1 port, opposite Quest).

And how far from its berthing point will it
need to station keep for the arm to go and grapple it ? couple of metres
? 10 metres ?

10 meters is a good guess. Has anyone seen any hard data on HTV
approach and grapple?

ATV/Soyuz/Progress use "targets" on the station to get Kurs to guide
their approach. Does the USA side have ay such targets to allow HTV to
guide itself to proper location an orientation to be grappled ?

ATV's approach can be aborted by a crew member on ISS, and ATV has an
auto-retreat system to get out of Dodge if the approach is botched.
Almost certainly, HTV will have the same setup, and can be aborted by
the crew member in the Cupola waiting to grapple it.

Brian

Brian Thorn wrote in
:

On Sun, 07 Dec 2008 22:00:43 -0500, John Doe wrote:

Does it really reduce flight software complexity ?

Yes, but not very much.

Seems to me that you
still need precise guidance, ability to stop and station keep (more so
with HTV since it will need to station keep very close to the station.

Where would HTV berth ?

Probably Node 1 nadir now that Node 3 won't be there (Node 3 is now
baselined for Node 1 port, opposite Quest).

HTV was never baselined for Node 3. It will be berthed at Node 2 nadir -
just like it has always been planned to be.

And how far from its berthing point will it
need to station keep for the arm to go and grapple it ? couple of
metres ? 10 metres ?

10 meters is a good guess. Has anyone seen any hard data on HTV
approach and grapple?

10 meters is about right. HTV has a "berthing box" they must remain
within in order for the SSRMS to capture it. The velocity requirements
are probably harder to meet than the position requirements.

ATV/Soyuz/Progress use "targets" on the station to get Kurs to guide
their approach. Does the USA side have ay such targets to allow HTV
to guide itself to proper location an orientation to be grappled ?

ATV's approach can be aborted by a crew member on ISS, and ATV has an
auto-retreat system to get out of Dodge if the approach is botched.
Almost certainly, HTV will have the same setup, and can be aborted by
the crew member in the Cupola waiting to grapple it.

HTV has two laser retroreflectors on the nadir surface of the JEM PM.

Bottom line is, the GNC systems needed to achieve the HTV berthing box
are just as sophisticated as the systems required to achieve the
ATV/Progress docking conditions.

There is no significant difference in risk between the systems, and they
are all markedly higher risk than Shuttle or Soyuz, which have crew
onboard. (Remote abort does no good if the spacecraft isn't listening to
you.)

"Jorge R. Frank" wrote in message
31...

There is no significant difference in risk between the systems, and they
are all markedly higher risk than Shuttle or Soyuz, which have crew
onboard. (Remote abort does no good if the spacecraft isn't listening to
you.)

Not that there have ever been problems in that area. :-)



--
Greg Moore
Ask me about lily, an RPI based CMC.

Listening in to the Russian side they always make sure that the progress is
capable of receiving the manual signal beforehand or they don't let it
anywhere near the iss as far as I can tell!

I'd hope the same is true of Htv etc.
I imagine the Mir experiences are engrained on many folk now..

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________


"Jorge R. Frank" wrote in message
31...
Brian Thorn wrote in
:

On Sun, 07 Dec 2008 22:00:43 -0500, John Doe wrote:

Does it really reduce flight software complexity ?

Yes, but not very much.

Seems to me that you
still need precise guidance, ability to stop and station keep (more so
with HTV since it will need to station keep very close to the station.

Where would HTV berth ?

Probably Node 1 nadir now that Node 3 won't be there (Node 3 is now
baselined for Node 1 port, opposite Quest).

HTV was never baselined for Node 3. It will be berthed at Node 2 nadir -
just like it has always been planned to be.

And how far from its berthing point will it
need to station keep for the arm to go and grapple it ? couple of
metres ? 10 metres ?

10 meters is a good guess. Has anyone seen any hard data on HTV
approach and grapple?

10 meters is about right. HTV has a "berthing box" they must remain
within in order for the SSRMS to capture it. The velocity requirements
are probably harder to meet than the position requirements.

ATV/Soyuz/Progress use "targets" on the station to get Kurs to guide
their approach. Does the USA side have ay such targets to allow HTV
to guide itself to proper location an orientation to be grappled ?

ATV's approach can be aborted by a crew member on ISS, and ATV has an
auto-retreat system to get out of Dodge if the approach is botched.
Almost certainly, HTV will have the same setup, and can be aborted by
the crew member in the Cupola waiting to grapple it.

HTV has two laser retroreflectors on the nadir surface of the JEM PM.

Bottom line is, the GNC systems needed to achieve the HTV berthing box
are just as sophisticated as the systems required to achieve the
ATV/Progress docking conditions.

There is no significant difference in risk between the systems, and they
are all markedly higher risk than Shuttle or Soyuz, which have crew
onboard. (Remote abort does no good if the spacecraft isn't listening to
you.)

"Brian Gaff" wrote in message
...
Listening in to the Russian side they always make sure that the progress
is capable of receiving the manual signal beforehand or they don't let it
anywhere near the iss as far as I can tell!

True.

I'd hope the same is true of Htv etc.
I imagine the Mir experiences are engrained on many folk now..

As the Mir/Progress collision showed, this isn't as ideal as being *on* the
docking craft looking out of a window. It's similar to landing a plane by
sitting in the cockpit looking out the windows versus landing a plane by
remote control. Hint: remote control is a lot harder (hardware, software,
and for the remote pilot). Having a person be (most of) your control system
is sometimes a lot easier than trying to completely automate or even
teleoperate.

An even better example might be in air refueling. The human workload there
is pretty high. You've got at least two pilots and a boom operator who all
have to be "on their toes" during the entire operation. That's a really
hard task to automate. I'm not sure if it's ever been done in an automated
or teleoperated fashion. I wonder if the USAF has experimented with in air
refueling of UAV's...

Jeff
--
"Many things that were acceptable in 1958 are no longer acceptable today.
My own standards have changed too." -- Freeman Dyson