Harwood AP CHEM Project

The shape of the bomb's reaction mass is critical to efficiency. The original project designed bombs with a reaction mass made of tungsten. The bomb's geometry and materials focused the X-rays and plasma from the core of nuclear explosive to hit the reaction mass. In effect each bomb would be a nuclear shaped charge. A bomb with a cylinder of reaction mass expands into a flat, disk-shaped wave of plasma when it explodes. A bomb with a disk-shaped reaction mass expands into a far more efficient cigar-shaped wave of plasma debris. The cigar shape focuses much of the plasma to impinge onto the pusher-plate.

In late 1958 to early 1959, it was realized that the smallest practical vehicle would be determined by the smallest achievable bomb yield. The use of 0.03 kt (sea-level yield) bombs would give vehicle mass of 880 tons. However, this was regarded as too small for anything other than an orbital test vehicle and the team soon focused on a 4,000 ton "base design".

The biggest design above is the "super" Orion design; at 8 million tonnes, it could easily be a city.[11] In interviews, the designers contemplated the large ship as a possible interstellar ark. This extreme design could be built with materials and techniques that could be obtained in 1958 or were anticipated to be available shortly after. The practical upper limit is likely to be higher with modern materials. Most of the three thousand tonnes of each of the "super" Orion's propulsion units would be inert material such as polyethylene, or boron salts, used to transmit the force of the propulsion units detonation to the Orion's pusher plate, and absorb neutrons to minimize fallout. One design proposed by Freeman Dyson for the "Super Orion" called for the pusher plate to be composed primarily of uranium or a transuranic element so that upon reaching a nearby star system the plate could be converted to nuclear fuel.

The Orion nuclear pulse rocket design has extremely high performance. Orion nuclear pulse rockets using nuclear fission type pulse units were originally intended for use on interplanetary space flights. Missions that were designed for an Orion vehicle in the original project included single stage (i.e., directly from Earth's surface) to Mars and back, and a trip to one of the moons of Saturn.[11] One possible modern mission for this near-term technology would be to deflect an asteroid that could collide with Earth. The extremely high performance would permit even a late launch to succeed, and the vehicle could effectively transfer a large amount of kinetic energy to the asteroid by simple impact. Also, such an unmanned mission would eliminate the need for shock absorbers, the most problematic issue of the design. Nuclear fission pulse unit powered Orions could provide fast and economical interplanetary transportation with useful human crewed payloads of several thousand tonnes.

Later studies indicate that the top cruise velocity that can theoretically be achieved by a Teller-Ulam thermonuclear unit powered Orion starship, assuming no fuel is saved for slowing back down, is about 8% to 10% of the speed of light (0.08-0.1c).[2] An atomic (fission) Orion can achieve perhaps 3%-5% of the speed of light. A nuclear pulse drive starship powered by Fusion-antimatter catalyzed nuclear pulse propulsion units would be similarly in the 10% range and pure Matter-antimatter annihilation rockets would be theoretically capable of obtaining a velocity between 50% to 80% of the speed of light. In each case saving fuel for slowing down halves the max. speed. The concept of using a magnetic sail to decelerate the spacecraft as it approaches its destination has been discussed as an alternative to using propellant, this would allow the ship to travel near the maximum theoretical velocity.[16]

At 0.1c, Orion thermonuclear starships would require a flight time of at least 44 years to reach Alpha Centauri, not counting time needed to reach that speed (about 36 days at constant acceleration of 1g or 9.8 m/s2). At 0.1c, an Orion starship would require 100 years to travel 10 light years. The astronomer Carl Sagan suggested that this would be an excellent use for current stockpiles of nuclear weapons.[17]

A concept similar to Orion was designed by the British Interplanetary Society (B.I.S.) in the years 1973–1974. Project Daedalus was to be a robotic interstellar probe to Barnard's Star that would travel at 12% of the speed of light. In 1989, a similar concept was studied by the U.S. Navy and NASA in Project Longshot. Both of these concepts require significant advances in fusion technology, and therefore cannot be built at present, unlike Orion. From 1998 to the present, the nuclear engineering department at Pennsylvania State University has been developing two improved versions of project Orion known as Project ICAN and Project AIMStar using compact antimatter catalyzed nuclear pulse propulsion units,[18] rather than the large inertial confinement fusion ignition systems proposed in Project Daedalus and Longshot.[19]

From 1957 until 1964 this information was used to design a spacecraft propulsion system called "Orion", in which nuclear explosives would be thrown behind a pusher-plate mounted on the bottom of a spacecraft and exploded. The shock wave and radiation from the detonation would impact against the underside of the pusher plate, giving it a powerful "kick". The pusher plate would be mounted on large two-stage shock absorbers that would smoothly transmit acceleration to the rest of the spacecraft.

USS Enterprise had eight A2W units of 26 shaft MW and was refuelled three times

Calculations showed that the fallout from a takeoff could be projected to lead to the premature death of between 1 and 10 people.

Project Daedalus

ICF uses small pellets of fusion fuel, typically lithium deuteride (6Li2H), with a small deuterium/tritium trigger at the center. The pellets are thrown into a reaction chamber where they are hit on all sides by lasers or another form of beamed energy. The heat generated by the beams explosively compresses the pellet, to the point where fusion takes place. The result is a hot plasma, and a very small “explosion” (compared to using a fission “bomb” to compress and heat the fusion fuel, as in a thermonuclear bomb).

This variant of a fusion rocket uses enormous electromagnetic fields as a “scoop” to collect and compress hydrogen from interstellar space.

High speeds force the reactive mass into a progressively constricted magnetic field, compressing it until thermonuclear fusion occurs.

To counter this, Bussard proposed ionizing these atoms at a safe distance using a laser beam, and using a powerful magnetic field to funnel the ionized atoms into the ship, bypassing the ship’s hull.

Let’s assume a constant acceleration of 1g during the first half of the ship’s journey, whereupon the ship decelerates to its destination at the same 1g for the comfort of all aboard. The resulting velocity of the ship for most of the journey would be very close to the speed of light. This would mean that the relativistic effects of time dilation come into play for the passengers.

For such a hypothetical voyage, Barnard’s Star—six light-years away—could be reached in a little under eight years, ship time. For longer voyages, even the center of our Milky Way galaxy could be reached in just 21 years.

those left behind on earth during such a hypothetical journey would perceive things very much differently. For them, millions of years would have passed.  Relativistic travels make distant interstellar space travel feasible—but only for those on board the voyage.

quinolone class of antimicrobials interferes with the maintenance of chromosomal topology by targeting DNA gyrase (topoisomerase II) and topoisomerase IV (topoIV), trapping these enzymes at the DNA cleavage stage and preventing strand rejoining

DNA strand breakage occurs after the drug has bound the enzyme

quinolone treatment is to generate double-stranded DNA breaks that are trapped by covalently (yet reversibly) linked topoisomerases whose functions are compromised

eads to bacteriostasis and eventually cell deat

DNA replication machinery becomes arrested at blocked replication forks, leading to inhibition of DNA synthesis, which immediately leads to bacteriostasis and eventually cell death

inhibition by quinolones induces the DNA stress response (SOS response), in which RecA is activated by DNA damage and promotes auto-cleavage of the LexA repressor protein, inducing expression of SOS-response genes including DNA repair enzymes

Preventing induction of the SOS response has also been shown to reduce the formation of drug-resistant mutants by blocking the induction of error-prone DNA polymerases34, homologous recombination20, and horizontal transfer of drug-resistance elements

ifamycin drugs inhibit DNA-dependent transcription by stable binding, with high affinity, to the subunit (encoded by the rpoB gene) of a DNA-bound and actively-transcribing RNA polymerase enzyme

a recently discovered class of RNA polymerase inhibitors (based on the compound CBR703) may inhibit elongation by allosteric modification of the enzyme

requirement of rifamycins is that RNA synthesis has not progressed beyond the addition of two ribonucleotides

bacterial cell is encased by layers of peptidoglycan (PG, or murein), a covalently cross-linked polymer matrix composed of peptide-linked β-(1–4)-N-acetyl hexosamine

β-lactams and glycopeptides are among the classes of antibiotics that interfere with specific steps in homeostatic cell wall biosynthesis

Successful treatment with a cell wall synthesis inhibitor can result in changes to cell shape and size, induce cellular stress responses, and culminate in cell lysis

penicillins, carbapenems and cephalosporins

inhibiting the peptide bond formation reaction catalyzed by transpeptidases, which are also known as penicillin-binding proteins

the β-lactam drug molecule (containing a cyclic amide ring) is an analog of the terminal D-alanyl-D-alanine dipeptide of PG, and acts a substrate for the enzyme during the acylation phase of cross-link formation –- which disables the enzyme due to its inability to hydrolyze the bond created with the now ring-opened drug

reduce cellular mechanical strength

chemically-modified glycopeptides have been shown to directly interact with the transglycosylase enzyme

lipopeptides (e.g., daptomycin) which affect structural integrity via their ability to insert into the cell membrane and induce depolarization

Filamentation can occur, following activation of the DNA damage responsive SOS network of genes

mRNA translation occurs over three sequential phases (initiation, elongation and termination) involving the ribosome

The ribosome organelle is composed of two ribonucleoprotein subunits, the 50S and 30S

Drugs that inhibit protein synthesis are among the broadest classes of antibiotics and can be divided into two subclasses: the 50S inhibitors and 30S inhibitors

0S ribosome inhibitors work by physically blocking either initiation of protein translation

or translocation of peptidyl-tRNAs, which serves to inhibit the peptidyltransferase reaction that elongates the nacent peptide chain

30S ribosome inhibitors

work by blocking the access of aminoacyl-tRNAs to the ribosome

LysisRupture of the cell envelope leading to the expulsion of intracellular contents into the surrounding

interferes with the stability of peptidyl-tRNA binding to the ribosome by inhibiting elongation factor-catalyzed translocation

promoting tRNA mismatching which can result in protein mistranslation