The development of the Delta second stage nitrogen tetroxide fueling system is briefly summarized. The nitrogen tetroxide fueling system and the equipment used to protect the spacecraft environment from the toxic nitrogen tetroxide fumes are described. Topics covered include: the nitrogen tetroxide transfer system; loading operations; safety precautions; and chemical treatment of all toxic vapors

Cross, T. M.

Grigsby, R. B.

Rucci, T. D.

English

NASA Technical Reports Server

DELTA
NITROGEN TETROXIDE
FUELING OPERATIONS
R. B. Grigsby, T. M. Cross, T. D. Rucci
National Aeronautics and Space Administration
March 30., 1978
183
https://ntrs.nasa.gov/search.jsp?R=19790012262 2020-03-21T22:59:42+00:00Z
INTRODUCTION
The Delta Program began as an interim measure in 1959 to
utilize existing launch vehicles for unmanned space projects. The initial
configuration combined the Thor IRBM and the Vanguard second and third
stages. The first launch attempt in May 1960 failed, but this was followed
three months later with the orbit of the Echo balloon, the first orbiting
spacecraft visible to the naked eye. The following vehicles, including that
which launched TELSTAR, the first active communications satellite, were suc-
cessful and NASA elevated the Delta Program to a permanent status. Since
that time, the launch vehicle configuration has been periodically upgraded
from a 100-pound synchronous orbit payload in 1960 to the present 2000-pound
synchronous orbit capability. The Delta evolution is shown in Figure 1.
At the present time Delta 140 (the one hundred fortieth Delta)
is being prepared to launch a Japanese experimental communications satellite
(BSE). Delta vehicles are also launched at Vandenberg Air Force Base in
California for polar launches such as required by the Nimbus and ITOS weather
satellites.
Today the majority of the Delta missions are reimbursable
launches for commerical. companies such as RCA, Intelsat, and Western Union;
for foreign governments like the Japanese BSE; or for other U.S. government
agencies, e.g., NOAA, the weather bureau. Thus, the program has progressed
from the research and development phase to one of applications, where the
184
spacecraft are used in everyday life for communications, weather, earth
resources, etc.
The Delta second stage nitrogen tetroxide fueling system, like
the parent Delta vehicle, has undergone an evolutionary process to reach
the present configuration, which will be discussed here. For instance,
the origin of the propellant trailers even precedes the Delta Program to
the Thor-Able Program of the 1959 timeframe. At that time and during the
early portion of the Delta Program, the propellents used were red fuming
nitric acid and Unsymmetrical Dimethyl Hydrazine (UDMH).
The original Delta second stage engine was a modified Aerojet
Vanguard second stage engine system. It was replaced with the Aerojet
Transtage engine which required that the propellant loading system be modi-
fied for N£04 and A50. The present second stage engine, a derivation of
the TRW Apollo LEM descent engine, also utilizes the same propellents.
Other modifications to the loading system have been made to
simplify it to meet more stringent safety criteria, and to assure that the
surrounding environment is protected. Particular emphasis has been placed
on assurance that the spacecraft environment is protected from the toxic
0^4 fumes.
The following will describe the ^04 fueling system and the
equipment used to insure the protection of the environment.
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N204 TRANSFER SYSTEM DESCRIPTION
The Delta second stage propellant loading system consists of
fuel (A50) and oxidizer ^ 264) transfer systems. These two systems are
essentially the same in design and function. In keeping with the symposium
topic, only the N204 transfer system will be considered in this paper.
Both are pressure fed, closed systems which utilize gaseous
helium, a storage tank pressurant, for liquid transfer. A closed system,
for the purpose of this paper, is defined here as a system in which all
toxic liquid and vapors are contained within the system and all venting is
accomplished through scrubbers containing a neutralizing solution. The
transfer systems are both manually and remotely controlled during loading
operations. Manual control is accomplished at the propellant transfer units
(PTU's) and upper mobile service tower (MST) levels. Remote operation of PTU
and MST valves is controlled from the propellant loading console (PLC) located
in the blockhouse. \
The N204 transfer system consists of the following major compo-
nents:
a. Mobile Trailers (PTU's)
b. Ullage Tank
c. Scrubber
d. Bubbler Tank
187
SYSTEM OPERATION
The second stage N204 loading system uses helium as a storage
tank pressurant for propel 1 ant transfer. During a loading operation the
storage tank is pressurized to 150 psig and an initial flow rate of 4 to 5
gpm established. This flow rate is maintained through the low flow orifice
until all ground and vehicle lines have been wetted and verified not leaking.
At this point the orifice bypass valve (4)* is opened and the flow rate
increases to approximately 20 gpm. When the vehicle tank is 95% full, a
slow fill of 5 gpm is then initiated by closing the orifice bypass (4)* and
filling until liquid is seen in the return line sightglass. The MST shutoff
valve (7)* is closed to stop propellent flow into the vehicle.
To obtain the correct vehicle tank gas ullage volume, a calculated
amount of liquid ^04 is drained back into the ullage tank. This allows for
thermal expansion of the vehicle propellant between loading and liftoff.
In order to drain this ullage tank the PTU supply tank is vented
by opening valve (2)* through the oxidizer scrubber which neutralizes the
contaminated gas. The vehicle is then isolated from the fill line by closing
valve (10)* and the ullage tank liquid is drained back down the tower into
the PTU supply tank by opening valves (7)* and (4)*. Both the fill and
return lines are then purged out and disconnected at vehicle points (10)*
and (11)*.
*See Schematic
188
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SAFETY PRECAUTIONS
A typical propellent loading begins with Pad Safety clearing
a 600-foot radius around the launch pad on which the loading is to be
carried out. Only fire, medical, and SCAPE support personnel are allowed
within this area during propellant flow and usually take up a position
approximately 500 feet west of the mobile service tower (MST). Manual
N204 loading operations at both the PTU and upper MST levels are carried
out by personnel dressed in SCAPE. The "buddy system" is used at all times
and the SCAPE crews are continuously monitored by a network of remotely
controlled TV cameras. In addition, constant voice communication is main-
tained between blockhouse and SCAPE personnel. Fuel and oxidizer loading
is controlled by a blockhouse test conductor and usually takes four to five
hours.
Prior to N£04 loading, the vehicle and transfer lines are leak
checked with helium to insure that they will not leak liquid which could
drip onto flight hardware. Drip shields are installed beneath the second
stage and vehicle propellent lines to protect the first stage from drip
damage in the event a leak would develop during loading. Neutralizer solu-
tion is also provided in the second stage area for washing off tools and
treating drip areas. High capacity water hoses for major spill control
are located at the PTU and upper MST levels. Fortunately, Delta has never
had a major spill.
190
Throughout ^0^ loading, SCAPE personnel are constantly
watching for visible evidence of leakage as well as monitoring an in-place
toxic vapor detector for leakage past the rocket engine flow control valve.
Loose hardware and tools are dipped in a bucket of neutralizer before.use
on the fuel system. At the completion of N£04 loading, SCAPE personnel dip
their gloves in neutralizer and shower in their suits before proceeding
into fuel loading. In addition, Pad Safety "sniffs" the area around the
2^^ 4 PTU and second stage for possible toxic fumes before giving permission
to proceed with fuel loading or opening the launch pad for normal work.
191
TOXIC VAPOR TREATMENT
Toxic vapor treatment on the Delta Program has evolved from
direct atmospheric discharge in the early part of the program to complete
containment and chemical treatment of all toxic vapors. The thrust toward
full containment was initiated by several factors, the most important of
which, in their chronological order, are payload protection, personnel
safety, and ecology. A water scrubber was initially used to reduce the
greatest concentration of vapors which occurs when the PTU supply tank is
vented. This scrubber satisfied most toxicity requirements for a number
of years. However, increased payload and safety restrictions necessitated
the replacement of the water scrubber with the chemical one now in use.
The following paragraphs describe toxic vapor treatment at the major system
component level .
PTU. The oxidizer PTU is filled with N204 at the fuel storage area
on the Cape. The PTU is filled to within one percent (8.5 gallons) of
overflow. A blanket pressure of 5 to 10 psig helium is then placed on the
PTU supply tank until it is raised to 150 psig for transfer to the vehicle.
After propel 1 ant transfer the supply tank is vented down to a blanket pres-
sure of again 5 to 10 psig, then disconnected from the MST and scrubber.
It is then transported back to the fuel storage area to be refilled for the
next launch. The. PTU dates back to the 1958 era and has undergone many
192
improvements since then. Most notable is the addition of the scrubber
and chiller units. Improved sealing and the reduction in leakage paths
have also resulted in its improved reliability. The PTU supply tank is
mounted inside of a catch tub which is designed to hold the entire tank
contents should it rupture.
Transfer Lines. All propellant transfer lines are purged with helium
for several minutes after use and before being disconnected from the second
stage and MST. The purging insures that all liquid NgAg. is blown back into
the PTU supply tank and toxic vapors routed to the scrubber for treatment.
Quick disconnect fittings installed in the transfer lines at the second
stage interface insure against loss of toxic vapor or liquid to the atmos-
phere. Hand valves installed in the transfer lines near the MST/PTU connect
point provide the same insurance at ground level. A caution sign is placed
on the transfer lines after they have disconnected as precaution against
inadvertent opening or disconnection of quick disconnects and hand valves.
A slight helium blanket pressure is left on the lines between launches.
Scrubber. jhe Delta N204 loading system is designed and operated in
a manner so as to minimize the venting of toxic vapors to the atmosphere.
To accomplish this all vapors are routed to a chemical scrubber before
escaping to the surroundings. The requirement for minimizing the venting
of reactive vapors had its origin more out of the protection of sensitive
payloads than environmental or safety aspects. With increased emphasis on
environmental protection, the system can meet essentially any discharge
requirement by reducing the flow rate through the scrubber.
193
The N204 scrubber was manufactured by the Peabody Engineering
Corporation of Stamford, Connecticut, for the McDonnell Douglas Astronautics
Company. Design specifications were that the scrubber "should be capable of
reducing 115,030 ppm N02 down to 500 ppm from 400 scfm for 15 minutes."
This value represents the maximum N02 concentration and supply tank vent
flow rate; however, actual concentration and vent down rates are considerably
less. The scrubber is a two stage design utilizing five percent sodium
bicarbonate solution as a vapor neutralizer.
It is a mobile unit which allows for easy transfer from one
launch pad to the other as well as permitting it to be towed to a contaminated
waste disposal area for draining. The unit stands approximately twelve feet
high and eight feet long. It consists of a 250 gallon neutralizer holding
tank at the base and a vertical spray column made up of four cylindrical
spray nozzle tray sections which are mounted one on top of the other. An
electric pump forces neutralizer from the holding tank to five nozzles located
in the spray column at 15 gpm and 20 psig.
^04 fumes from the PTU supply tank, vehicle oxidizer tank, and
the ullage tank, as well as from other sources, enter the scrubber through a
header located at the top of the holding tank. As the vapors migrate toward
the spray column they are partially neutralized by the sodium bicarbonate
liquid solution in the first stage of scrubbing. Next, vapors pass through
the cylindrical nozzle tray sections where the toxic concentration is reduced
in stages until an acceptable level is reached for release to the atmosphere.
194
Bubbler Tank. After completion of fuel and oxidizer loading the
scrubber is disconnected from the MST and PTU and removed from the launch
pad area in order to protect it from rocket motor exhaust at liftoff. In
its place a bubbler tank on the umbilical tower provides for toxic vapor
treatment until launch. The bubbler tank is essentially a six-inch diameter
piece of stainless steel pipe six feet long. It is filled with a 5% solution
of sodium bicarbonate. Vapors from the second stage ^04 tank enter the
bottom through a diffuser and migrate upward toward a vent located on the
end cap at the top. Vent flow rates and volumes are low and experience with
this unit indicates no detectable toxic vapor in the area of the bubbler tank
vent. This method of venting is only used for ^64 tank pressure level adjust-
ment or in case of an emergency vent. A typical pressure adjustment operation
due to N£04 expansion in the tank would result in venting approximately
150 sci of N204 vapor through the bubbler tank, an amount easily neutralized
by this technique. The bubbler tank solution is checked for sodium bicarbonate
concentration after every launch.
195
CONCLUSION
Environmentally speaking, the payload requirements for
emission control are more stringent than those allowed by various safety
and environmental organizations. The present sodium bicarbonate scrubber
meets these requirements at Complex 17. The elaborate safety precautions
surrounding a Delta propellant loading operation are for personnel safety
because of the potentially high explosive yield of N204 and Aerozine 50
when they are brought in close proximity to one another.
196


Delta nitrogen tetroxide fueling operations

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